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Osea, officially the Osean Federation (オーシア連邦), is a large country and international superpower located on the Osean continent. Osea encompasses a majority of the continent's western landmass, and shares land borders with Belka, Ustio, and Sapin to the east, and an unknown country to the south. Its capital, Oured, is located on the tip of Osea's southeastern peninsula near Oured Bay.

Osea is a highly developed country that possesses a large population, extensive infrastructure, thriving economy, and well-outfitted military force. Osea is also considered one of the world's foremost leaders in aeronautics and space-exploration development. Its achievements include the construction of the Arkbird (a joint program with Yuktobania), the Strategic Orbital Linear Gun, and the Arsenal Birds.

By virtue of its world power, Osea also holds expansionist ideologies. It has been involved in multiple conflicts with the countries to its east, most notably Belka during the Osean War of 1905–1910 and the Belkan War of 1995. It has also attempted to annex southern Usean countries through the Spring Sea Treaty, which failed due to the Usean Continental War.

Osea is the player character's homeland in Ace Combat 5: The Unsung War and an allied country in Ace Combat Zero: The Belkan War. The player will be allied with Osea (to an unknown extent) in Ace Combat 7: Skies Unknown.


Early history (–1905)

A view of the Osean capital, Oured

The country of Osea is known to have existed prior to the 20th century. According to navigational charts from the early modern era, several Osean cities, such as Oured and Bana City, have existed for quite some time.[1]

Osean War (1905–1910)

Between 1905 and 1910, Osea and Belka entered open war. Over the next five years, Belka became the first country to use aircraft for warfare. Osea followed suit, matching the newly-created Belkan Air Force with the Osean Air Defense Force.[2]

Cold War (1980s–1995)

Over the course of the mid-20th century, Osea flourished and began to expand its political influence around the globe. By the 1980s, Osea was in the midst of a cold war with the Union of Yuktobanian Republics, its rival superpower across the Ceres Ocean.[3] The ongoing arms race compelled Osea to develop atmospheric weapon systems under the Strategic Defense Initiative to counter Yuktobania's recent developments in missile technology.[4] This led to the construction of the Strategic Orbital Linear Gun (SOLG), a massive Kinetic Energy Weapon that would drop shells from orbit to destroy missile silos.[5] The concept of a "maneuverable orbiting spacecraft" was also created under the Strategic Defense Initiative.[4]

As part of the Cold War, Osea began to heavily expand its military, particularly its Air Force, by acquiring new recruits.[6][7] Osea's Rearmament Declaration in October 1990[3] shifted around some of its personnel between the branches, and created new units. The most notable example was the creation of the Wizard Squadron and its secondary unit, the Sorcerer Squadron. Austin Winters, a member of the Osean Army, was transferred to the Sorcerer Squadron[8] alongside Anthony Palmer[6] and Todd Barry.[7]

Around this era, Osea was also surveying the world for potential troves of natural resources. Looking eastward, Osea had reason to believe that underground resources were present in Belka's southeastern region, the area now known as Ustio. Belka was undergoing economic turmoil at the time, so Osea took advantage of the situation. The country helped push for Ustio's independence, which was successful in May 1998.[9][10] Osea also purchased pieces of land from Belka, most notably the Five Great Lakes and intersecting islands between the two countries. This brought several Belkan cities such as Wesson and Rutherford under Osean control.[11]

Osea offered a joint expedition with Belka to explore potential natural resources around the Five Great Lakes, where Belka would get to share the profits. Belka agreed, but the company quickly collapsed; Osea had exaggerated on the amount of resources in the region, and Belka's economy was further destabilized. Anti-Osean sentiment heavily grew within Belka as a result.[12][10]

Belkan War (1995)

OBC graphic showing the extent of the Belkan invasion and the Allied Forces counterattack


In March 1995, Belka declared war on all of its neighbors and invaded much of the territory Osea had acquired in the Great Lakes sale. In response, Osea created the Allied Forces, a temporary alliance between Osea and two other countries Belka had invaded: Ustio and Sapin.[11] Surprisingly, Yuktobania joined the Allied Forces as well, which began the process of reconciliation between Osea and Yuktobania.[13] The Allied Forces signed a nonaggression treaty, agreeing to only act in self-defense and not to invade Belkan territory.[14]

On April 24, Osea launched Offensive Campaign No. 4101 with its 3rd Osean Naval Fleet (including the OFS Kestrel, which was undergoing sea trials) to capture the Futuro Canal and open a sea route into Belka.[15] From there, Osea's 101st and 122nd Airborne Divisions, supported by Ustio's mercenary Galm Team, performed a paratroop operation to secure Solis Ortus[16] and liberate Directus, the capital of Ustio.[17] In the meantime, Osea accelerated development of the SOLG,[18] presumably to use it against Belka and end the war quickly.

Invasion into Belka

In late May, Osea received intel that Belka was developing a new weapon of mass destruction known as V2. Using V2 as casus belli for self-defense, Osea spearheaded an invasion into Belkan territory.[19] Belka used the Excalibur laser tower in retaliation against the invading troops, prompting the Allied Forces to send Galm Team and Crow Team to destroy Excalibur.[20]

On May 28, the Allied Forces permanently abrogated the nonaggression treaty at the Assembly of Nations, and simultaneously launched an assault to capture Area B7R, a strategic and symbolic area for Belka. With the help of Galm and Crow Teams, despite Belkan reinforcements, the Allied Forces captured B7R.[14] Osea then performed a bombing raid on Hoffnung to cripple Belka's industrial power,[21] and began marching through the Waldreich Mountains towards Sudentor.[22]

Cessation of hostilities

During a skirmish at Sudentor on June 6, Belka detonated seven nuclear warheads in the Waldreich Mountains, killing over 12,000 civilians.[22][23] Osea, the other Allied Forces members, and Belka agreed to an immediate cease-fire. Despite remnant resistance over the next month, the Allied Forces and Belka signed a treaty in Lumen to officially end the Belkan War on June 20.[24] The treaty was one-sided and heavily favored Osea;[25] the country annexed the entire state of South Belka and renamed it "North Osea".[26] Historically Belkan cities, such as Lumen and Sudentor, were now assimilated by Osea,[25] and the South Belka Munitions Factory was renamed to "North Osea Gründer Industries".[27] Over the next ten years, Osea would begin tracking down every member of the Belkan Air Force, adding them to a database and attempting to capture war criminals and dangerous people.[28]

A terrorist organization, A World With No Boundaries, began operations against Osea and the other Allied Forces members in December 1995,[29] prompting an immediate counterattack. Osean pilots joined the Galm Team in striking against the organization at Avalon Dam,[30] and Cipher, Galm Team's flight lead, helped to destroy the V2 missile that they tried to launch.[31] Osea's investigation into the Belkan Air Force expanded into investigating A World With No Boundaries members.[32]

Era of peace (1996–2010)

"The world was once again at peace. And, thanks to them, it seemed it would last forever."
Albert Genette[33]

In 1996, Osea signed a bilateral agreement with Yuktobania that officially ended the Cold War. The treaty signing compelled the survivors of the OADF's Wizard Squadron to plot the Osean president's assassination, but they were either killed or arrested by Osean Special Ops.[34]

Ulysses and Usean treaty

On April 20, 1996, the Federation of Central Usea announced the existence of the Ulysses 1994XF04. Refugees began immigrating out of the Usean continent; Osea's capital, Oured, accepted the largest number of refugees compared to other cities.[35] Osea expressed desire to assist Usea in building Stonehenge but could not due to post-Belkan War reconstruction.[4][36]

The next year, a group of southern Usean countries decided to join the Osean Federation. Despite backlash from their neighbors, Osea extended an offer of military allegiance, known as the Spring Sea Treaty. The treaty was to be signed on May 30, 1997, but that day, extremist terrorists took control over the entire continent. The ensuing Usean Continental War implied that Osea ultimately did not sign the treaty.[37]

The next year, Osea acquired some Belkan Air Force pilots to work as aggressor units for the country.[36] This included the Grabacr Squadron, referred to as the "8492nd Squadron" in Osea.[38]

Creation of the Arkbird

Following the Ulysses planetfall in July 1999, the remaining meteors stuck in Earth's atmosphere became a threat to satellites along with the potential that they could strike outside of the Usean continent. Osea decided, with Yuktobania's assistance, to create the Arkbird out of the "maneuverable orbiting spacecraft" concept from the Strategic Defense Initiative in the 1980s. The Arkbird was outfitted with a laser on top that could not physically attack anything below the spacecraft, which would be used to destroy Ulysses fragments. By 2008, the Arkbird had already vaporized over 80% of the remaining Ulysses fragments. In cooperation with other countries, Osea and Yuktobania also proposed an International Space Station.[4]

In 2004, Vincent Harling was elected as the 48th President of the Osean Federation.[36] Throughout his first term, Harling's peace policies strengthened Osea's ties to Yuktobania and led to the creation of Basset Space Center.[39] In 2008, Harling was reelected to a second term.[13] That year, Osea hosted the G7 Summit aboard the Arkbird. Osea personally invited the provisional government of Erusea to help promote peace on the Usean continent. The meeting saw an historic push to ratify several anti-proliferation treaties, including a Strategic Arms Reduction Treaty and a Comprehensive Nuclear Test Ban Treaty. The move was seen as a further strengthening of bonds between Osea and Yuktobania, as well as the nations of the world.[4]

Circum-Pacific War (2010)

Initial attacks

In late September 2010, Osea experienced a series of airspace intrusions by Yuktobanian Air Force aircraft shortly before its former ally declared war on September 27, 2010.[40] Over the coming days, Osea fended off several Yuktobanian airstrikes.[41][42] The Yuktobanian submarine Scinfaxi sank the OFS Vulture and Buzzard aircraft carriers, prompting Osea to install an air-to-ground laser module on the Arkbird.[43] The combined power of the Arkbird and Wardog Squadron sank the Scinfaxi off the shore of Sand Island Air Force Base.[44]

On October 22, President Harling attempted to meet with Yuktobanian Prime Minister Seryozha Viktrovich Nikanor in the neutral country of North Point. However, Harling's transport plane, Mother Goose One, was forced to make an emergency landing with the help of Wardog Squadron after the plane was shot at by friendly SAM defenses and an onboard spy shot the pilots. The 8492nd Squadron relieved Wardog Squadron[45] but captured Harling and presumably killed the others onboard.[46] At the same time, a bomb carried aboard a shipment to the Arkbird disabled its power generator, preventing it from being used any further.[47]

Invading Yuktobania

Following these events, the hawkish Vice President Appelrouth usurped control of the Osean government and sanctioned a full-scale ground invasion of Yuktobania in November.[48] In the midst of the assault, a Yuktobanian engineering college was fired upon by aircraft identified as Osean.[49] In retaliation, Yuktobanian commandos performed two simultaneous terrorist attacks within Osean territory.[50][51] Osea then sanctioned deep-strike operations against Yuktobanian military bases,[52][53] and the Wardog Squadron sank the Hrimfaxi in the Razgriz Straits, earning them the "Demons of Razgriz" nickname.[54]

Later that month, the Vice President hosted a ceremony in November City with Wardog doing a flyby. The ceremony was attacked by Yuktobanian aircraft, and the 8492nd Squadron temporarily called off Osea's reinforcements, forcing Wardog Squadron to defend the stadium on their own. Wardog's Alvin H. Davenport was shot down and killed in the battle before reinforcements finally arrived.[55]

Shortly after the fall of Cruik Fortress on December 6, Wardog was exposed as traitors and summarily executed while attempting to escape over the northern Ceres Ocean.[38] Following these events, the Osean Army was unable to capture the Yuktobanian capital of Cinigrad and became stalemated with the Yuktobanian forces.

In late December, President Harling returned to the capital and regained control of his office from Appelrouth.[56] On December 30, Harling hosted a televised press conference with Yuktobanian Prime Minister Nikanor and revealed that the war had been orchestrated by an unspecified group, which planned to use a weapon of mass destruction against the two nations.[57] With the war officially over, a coalition force of Osean and Yuktobanian fighters and ground troops attacked Sudentor, North Osea to halt the Belkans' plans to commit mass murder. The Belkans were ultimately defeated by Razgriz Squadron, and Osea was spared.[58][59]

For several years after the war, the circumstances behind the "Belkan Conflict" were kept secret by the Osean government. Four years later, Harling announced at the 2014 Osean Federation Council meeting that all information pertaining to the war would be released to the public in 2020. It is presumed that Osea, under Harling's leadership, worked to reestablish the alliance Osea and Yuktobania had shared prior to the war.[60]

Osea-Erusea Conflict

At some point after the conflict, the Osean Federation became engaged in combat with the reformed Kingdom of Erusea for, as of yet, unknown reasons.[61]


Political structure

One of the largest nations of the Osean continent, the Osean Federation is a democratic federal state divided into six administrative regions: Burton, Glennon, Stockham, Lindsey, Rinehart, and Eversole, the last of which serves as the capital district.[62] The Osean populous is represented in a legislative body known as the Osean Federation Council. The national government is headed by a popularly elected president who assumes the executive office for a four-year term; it is unknown if the Osean presidential office carries a term limit.

The Osean government includes roles such as Vice President[55] and Foreign Minister[12]; governmental departments include the Ministry of Defense and the Osean Aeronautics and Space Administration.[4]

Armed forces

Osea supports one of the largest and most well-equipped military forces in the world. Known as the Osean Defense Forces, the nation's military is comprised of the Osean Air Defense Force, the Osean Maritime Defense Force (which supports a marine division), the Osean Army, and Osean Coastal Defense Force.



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