Complex sentence: By April 1916, the air superiority established by the Eindecker pilots in the Fokker Scourge had long gone and the Eindeckers themselves were giving way to the Fokker and Halberstadt D-series biplane fighters.
Split into simpler sentences: By April 1916, the air superiority established by the Eindecker pilots in the Fokker Scourge and had long gone. The Eindeckers themselves were giving way to the Fokker and Halberstadt D-series biplane fighters.