Complex sentence: The first large wave arrived in the 1960s and 1970s as part of the German economic plan of "Gastarbeiter"; as Germany was seeking immigrant workers (largely from Turkey), many Assyrians/Syriacs saw an opportunity for freedom and success and applied for visas.
Split into simpler sentences: The first large wave arrived in the 1960s and 1970s as part of the German economic plan of "Gastarbeiter". As Germany was seeking immigrant workers (largely from Turkey), many Assyrians/Syriacs saw an opportunity for freedom and success and applied for visas.