Complex sentence: The Selay have been enemies of the Anticans since their first encounter, however Federation diplomats were able to mediate to resolve their differances and now both the Selay and the Anticans are members of the Federation.
Split into simpler sentences: The Selay have been enemies of the Anticans since their first encounter. However, Federation diplomats were able to mediate to resolve their differences; now, both the Selay and the Anticans are members of the Federation.