Complex sentence: After the Spanish had made their presence known for some years, the Xiu Maya state of the western half of the peninsula allied itself with the Spanish Empire, which subsequently inflicted massive property and population losses upon the Iz'a Maya state.
Split into simpler sentences: After the Spanish had made their presence known for some years, the Xiu Maya state of the western half of the peninsula allied itself with the Spanish Empire. This alliance subsequently inflicted massive property and population losses upon the Iz'a Maya state.