What is Popular Sovereignty?

Also called sovereignty of the people, popular sovereignty is the doctrine that the people's will is supreme. It's the people who are the source of political power, as, it is they who elect their representatives.
Popular sovereignty was a political doctrine that gained popularity before the American Civil War, a turning point in American history. The concept was first coined in the latter half of 1840s by Stephen Douglas, the presidential candidate in the general elections of 1860. He was of the opinion that the settlers should be given the right to vote about their status in the early days of territorial development. However, there were others who had differing opinions, and these people were of the view that the vote should be taken as and when the territory was completely ready for statehood. It was in the Kansas-Nebraska Act and the Compromise of 1850 that sovereignty of the people was first invoked.
One of the major issues of 19th century United States was the problem of slavery. Instead of solving the issue and confronting it head on, the leaders of the federal government avoided a debate and tried to get to a compromise solution by advocating popular sovereignty. They were of the view that the people should decide for themselves whether slavery should be permitted in their states or not.
Popular Sovereignty in the Constitution
It was during the times of slavery that this concept gained momentum, and was later adopted in the constitution of the United States of America. The constitution states that the citizens of the country have the sovereign rights to create a government which would be responsible to them. It means that, the citizens of the country are supreme, and it's the people who authorize their representatives to run their lives. In short, the government of the day derives its power from the people.
The American Revolution marked the beginning of an independent nation, free from the rule of the British Crown, which represented the bonds of slavery. The 13 states together formed a sovereign state and declared independence, and formed the Republican form of government. Under this type of government, the citizens of the country were declared as sovereigns. The government of the states were created to serve the people, and the federal government was elected by the people to serve the interests of the state. That's to say the federal government was indirectly responsible for the welfare of the people, and they served the people through the states.
Examples of Popular Sovereignty
To have a clear understanding of the subject in question, the relationship between popular sovereignty, power, and state, should be understood. Power means the ability, whether it's moral, social, military, legal or political, to influence the actions of a political actor by another. So, whenever a particular nation tries to influence or oppress another sovereign state, it's an attack on the popular sovereignty of another nation. A good example here is the invasion of Kuwait by Iraq. Iraq, on its part, tried to exert its power over the rights of the citizens of another nation, which endangered the popular sovereignty of Kuwait. The basic idea is that, the identity of the people of a state should be protected and safeguarded from oppression.
Thus, popular sovereignty is used to signify the will of the people. There was a lot of debate on this concept, especially before the Civil War, but today, it is enshrined in the constitution of the United States of America.