The correct answer is the Union's attempt to give resources and supplies to Fort Sumter.
Fort Sumter was an American military fort in South Carolina. After the state of South Carolina seceded just a few short weeks after the presidential eleciton of 1860, the fort remained under the control of the US government. A few months after secession, the South Carolinians had not interfered with the Fort nor were planning on attacking this fort.
However, tensions would rise when the Union sent more supplies and troops to this fort. The government of South Carolina as the Union preparing for war. The Confederacy attacked Fort Sumter, leading to the first battle of the US Civil War.
It was a strategy created by the Union, the goal was to defeat the rebellion by blockading southern ports and controlling the Mississippi river
Construction of the Great Wall of China was started in approximately 221 B.C. Construction continued on and off until 1500A.D. The construction was ordered by Emperor Qin Shihuang. the eastern section of the wall uses stones,lime and rocks while the western part is built of mud and grass.