Complex sentence: When East Germany joined West Germany on 3 October 1990, the West German identity card was introduced in the former East German territory; unexpired East German identity cards could still be used until 31 December 1995.
Split into simpler sentences: When East Germany joined West Germany on 3 October 1990, the West German identity card was introduced in the former East German territory. However, unexpired East German identity cards could still be used until 31 December 1995.