Complex sentence: Some of the more famous keynote speeches in the United States are those made at the party conventions during Democratic and Republican presidential campaigns and were by Steve Jobs at Apple product, system and service launches.
Split into simpler sentences: Some of the more famous keynote speeches in the United States are those made at the party conventions during Democratic and Republican presidential campaigns. In the commercial arena, Steve Jobs delivered some of the most influential keynote speeches at Apple product, system and service launches.