Complex sentence: In 2398, the Capellan Confederation declared war on the League in an attempt to annex the Andurien system and other surrounding systems would the beginning of the 150-year period known as the Age of War.
Split into simpler sentences: In 2398, the Capellan Confederation declared war on the League in an attempt to annex the Andurien system and other surrounding systems. The ensuing conflict (the First Andurien War) sparked the 150-year period known as the Age of War.