Oskar was born to Maximilian Josef and Sabine von Altenheim, descendants of an influential aristocratic family whose roots stretched back to the medieval Belkan kingdom, in the northern coastal town of Anfang. His father was a retired major general of the Belkan Army and a veteran of both the Osean War, in which he fought as a young enlisted soldier, and the Belkan Expansion Conflict. It was no surprise to anyone that Maximilian Josef wanted Oskar to follow his footsteps. The older Altenheim raised his son to be a Belkan patriot and a good fighter, and Oskar embraced it fully. His father trained Oskar in marksmanship and hand-to-hand combat from an early age, and also encouraged his interest in history (especially Belkan history), as well as geography. When he turned 13, Oskar von Altenheim ended up joining a local military school in Anfang. There, he excelled, proving himself to be a skilled marksman and martial artist, as well as a brilliant strategist.
Altenheim ended up graduating from the military school as the third in his class in June 1974, commissioned as an infantry officer. As a platoon leader in the 8th Infantry Division, Third Army, Second Lieutenant Altenheim was deployed with his unit to fight in the Rectan War.
The Rectan War (1975―78)
Tensions with various countries bordering Belka had been present throughout the mid 20th century, which boiled over in the 1970s with the military invasion of Recta. The Belkan Army advanced over the border into Recta with air cover provided by the Belkan Air Force. Altenheim and his unit in the 8th Infantry Division were among the first to enter the country, easily overpowering the inexperienced Rectan border guard and army formations. During the initial fighting, Altenheim led his platoon in a charge to capture an enemy artillery position. When his second in command refused to follow him, he pointed his pistol at him told the man, "If you don't follow me, I'll shoot you." The sergeant complied, and the platoon seized control of the Rectan artillery position. For that accomplishment, Altenheim was promoted to full lieutenant.
However, the Belkan Air Force failed to secure air superiority, and the Rectan Air Force began bombing the Belkan ground units. It halted their advanced, and Altenheim's platoon took considerable losses from the attacks. The man himself was wounded in the chest but tried to continue to lead his unit personally, while the medics were tending to him. Eventually, the ace pilot Dietrich Kellerman and his Silbur Squadron managed to defeat the Rectans and allow the Belkan ground forces to advance. The Third Army was involved in the offensive operation to take the main Rectan resistance stronghold of Calle City. The 8th Infantry fought in fierce house-to-house battles, and having nearly recovered from his wounds, Altenheim took part in it as well. Their platoon cleared out an number of enemy-controlled buildings, during which the Belkan soldier gained a grudging respect for ferocity of the Rectans. Despite the fierce Rectan resistance, the city fell to the Belkans.
Over the course of the war, Altenheim also came to know several other officers who would become his friends and colleagues over the next several years. Among those were Second Lieutenants Erich Warburg and Jochen von Below, other platoon leaders from the 8th Infantry whom he met and fought with during the Battle of Calle City. Another was Lieutenant August Scheer, a skilled tank driver who became a tank ace during the war, a member of the 4th Panzer Division that he met during the early combat. Less than a week after the victory at Calle City, the war was though to be over, as the First and Second Armies had taken the Rectan capital city of Cor. However, a group known as the Rectan Liberation Front continued to put up resistance against the Belkan occupation forces.
Altenheim was promoted to captain after the fall of the capital, though out of anger at the enemy for the death of so many of his platoon's soldiers, he volunteered for another tour of duty in the country. His unit saw some action against Rectan insurgents, though (much to his dismay) the 8th Infantry Division was mostly used as a garrison force for the capital and was away from much of the fighting. In 1978, the group was finally defeated and its leaders were killed, allowing Altenheim to return to the homeland.