Complex sentence: The Austrian government consigned him to organize the "International Philatelic Exhibition in Vienna" ("WIPA 1933"), which was one of the biggest philatelic exhibitions before World War II. Because of the great success of the WIPA he was decorated.
Split into simpler sentences: The Austrian government consigned him to organize the "International Philatelic Exhibition in Vienna" ("WIPA 1933"). This was on of the biggest philatelic exhibitions before World War II. Because of the great success of the WIPA he was decorated.