Complex sentence: Texas had declared its independence in 1836 but Mexico did not recognize its independence, in Yucatán, a similar rebellion had begun and was fought off-and-on from 1836 to 1846.
Split into simpler sentences: Texas had declared its independence in 1836 but Mexico refused to recognize it. In Yucatán, a similar rebellion had begun and was fought off-and-on from 1836 to 1846.