Complex sentence: In the early 1900s the state-of-the-art in ammunition technology was defined by the advent of smokeless powder; older blackpowder ammunition was in the process of being converted to smokeless.
Split into simpler sentences: In the early 1900s the state-of-the-art in ammunition technology was defined by the advent of smokeless powder. Older blackpowder ammunition was in the process of being converted to smokeless.