Complex sentence: Always seeking new and better technology, the Twelve Colonies created the Cylons-highly intelligent robots designed to make human lives easier; however, the Cylons rebelled against their human masters, causing the war.
Split into simpler sentences: Always seeking new and better technology, the Twelve Colonies created the Cylons-highly intelligent robots designed to make human lives easier. However, the Cylons rebelled against their human masters, causing the war.