Complex sentence: Some Avias ended up in the German "Luftwaffe" when parts of Czechoslovakia was absorbed into Germany in 1939, others where sold to the Slovakian and Bulgarian air forces.
Split into simpler sentences: Some Avias ended up in the German "Luftwaffe" when parts of Czechoslovakia were absorbed into Germany in 1939. Other aircraft were sold to the Slovakian and Bulgarian air forces.