Complex sentence: Using this windfall and other sources of information, the French adapted Plan "XV" in 1906, to be ready for a German invasion of Belgium and subsequent plans contained increases in the forces to be assembled to the north and north-east of Verdun.
Split into simpler sentences: Using this windfall and other sources of information, the French adapted Plan XV in 1906, to be ready for a German invasion of Belgium. Subsequent plans contained increases in the forces to be assembled to the north and north-east of Verdun.