Final answer:
The Southern states lost the war, their way of life, and their plantations. They are resentful because they believe secession was not illegal and feel the North used its military might to label them as traitors. Additionally, some Southerners are resentful because they lost their power over slaves.
Step-by-step explanation:
The Southern states lost several things during and after the Civil War. Firstly, they lost the war itself, as they were defeated by the Union forces. Secondly, they lost their way of life, which was primarily based on the institution of slavery. Lastly, many Southerners lost their plantations, which were often their main source of wealth and power.
The reason why the Southern states were so resentful is multifaceted. Firstly, they believed that secession was not illegal and that they had the right to govern themselves. Secondly, many Confederates felt that the North was able to label them as traitors not because of constitutional authority, but because of their superior military strength. Thirdly, some Southerners were resentful because they no longer had slaves to exert power over, and they viewed this loss of control over black people as a significant blow to their social status.