Complex sentence: The fort was reinforced by troops and material sent by Montgomery C. Meigs, an Army engineer tasked by President Abraham Lincoln and Secretary of War Seward to draw up a plan to reinforce Fort Pickens.
Split into simpler sentences: The fort was also reinforced by troops and material sent by Montgomery C. Meigs. This Army engineer was tasked by President Lincoln and Secretary Seward to draw up a plan reinforcing Fort Pickens.