Complex sentence: Though he was concerned with proliferation of high rise buildings in urban environment, he was an admirer of such buildings (built in USA) and supported building of such structures in Germany even though the purists of German traditional architecture opposed this practice.
Split into simpler sentences: Though he was concerned with proliferation of high rise buildings in urban environment, he was an admirer of such buildings built in USA. He supported building of such structures in Germany even though the purists of German traditional architecture opposed this practice.