Complex sentence: The Mexican army succeeded in defeating most of the Maya population of the region during the 1910s, and in 1915 the area was again declared to be legally part of the state of Yucatán.
Split into simpler sentences: The Mexican army succeeded in defeating most of the Maya population of the region during the 1910s. In 1915 the area was again declared to be legally part of the state of Yucatán.