Complex sentence: After the war, it became clear that the Soviets were disinclined to return the Eisenach facility to BMW, giving rise to the irony whereby BMW automobiles produced between 1946 and 1951 were produced outside the control of BMW in Munich.
Split into simpler sentences: After the war, it became clear that the Soviets would not return the Eisenach factory to BMW. BMW-branded automobiles produced between 1946 and 1951 were therefore being produced outside the control of BMW headquarters in Munich.