Complex sentence: Reaching France in 911, Rollo and his men besieged Paris and Chartres, and as a compromise with King Charles the Simple, they were granted the fiefdom of Normandy in exchange for Rollo and his men defending the shores of the Seine river against all invaders.
Split into simpler sentences: Reaching France in 911, Rollo and his men besieged Paris and Chartres. Reaching a compromise with King Charles the Simple, they were granted the fiefdom of Normandy in exchange for an agreement to defend the shores of the Seine river against all invaders.