Civil War was the most costly war America ever fought; it lost more men in that war alone than it did in any of its other wars combined. The issues that caused the Civil War had been brewing since the United States was formed. The most important causes Southerners listed for the wars were unfair taxation, states' rights, and the slavery issue.
Southerners felt that the Federal government was passing laws, such as import taxes, that treated them unfairly. They believed that individual states had the right to "nullify", or overturn, any law the Federal government passed. They also believed that individual states had the right to leave the United States and form their own independent country. Most people in the North believed that the concepts of "nullification" and "states' rights" would make the United States a weaker country and were against these ideas. The history and economy of the North were very different from those of the South.
Factories developed in the North, while large cotton plantations developed in the South. The Southern plantation owners relied on slave labor for economic success. Their crops were sold to cotton mills in England, and the ships returned with cheap manufactured goods produced in Europe. By the early 1800s, Northern factories were producing many of those same goods, and Northern politicians were able to pass heavy taxes on imported goods from Europe so that Southerners would have to buy goods from the North. These taxes angered Southerners.
Abolitionists in the North wrote books, published newspapers spreading their ideas about slavery, and often assisted slaves to freedom when they ran away from their masters. Southerners believed that abolitionists were attacking their way of life and that the Federal government was not doing enough to protect their "property" from running away. Southerners were also...