Complex sentence: These events marked the first time under the new constitution that the federal government used strong military force to exert authority over the states and citizens and is also the only time a sitting U.S. president personally commanded troops in the field.
Split into simpler sentences: These events marked the first time under the new constitution that the federal government used strong military force to exert authority over the states and citizens. It was also the only time a sitting U.S. president would personally command troops in the field.