Complex sentence: Gilpin advocated a march on Mexico City and convinced a majority of officers, but Doniphan subverted this plan, then in late April Taylor ordered the First Missouri Mounted Volunteers to leave Chihuahua and join him at Saltillo.
Split into simpler sentences: Gilpin advocated a march on Mexico City and convinced a majority of officers, but Doniphan subverted this plan. Then in late April, Taylor ordered the First Missouri Mounted Volunteers to leave Chihuahua and join him at Saltillo.