Complex sentence: During the Mexican War of Independence, the intelligentsia of Yucatán watched the events to the north, and following 1820 organized their own resistance to Spain, forming the Patriotic Confederation, which declared its own independence from Spain in 1821.
Split into simpler sentences: During the Mexican War of Independence, the intelligentsia of Yucatán watched the events to the north. Following 1820 they organized their own resistance to Spain, forming the Patriotic Confederation, which declared independence from Spain in 1821.