The militia movement refers to a belief that citizens of the United States need to form themselves into armed militias to defend their constitutional rights. This idea experienced a sudden growth in popularity during the mid-1990s in response to what its proponents perceived as a change in the nature of American government. Many different groups are part of this movement, but the only unifying idea among them is a distrust of the federal government.
The second amendment of the United States Constitution is what makes the militia movement possible. This law protects the right of American citizens to bear arms, and makes reference to the existence of well-regulated militias. The members of the militia movement interpret this law to mean that citizen militias are necessary to fight against the American government, if it oversteps its constitutional bounds or threatens the rights of its populace. There is no single consensus within the militia movement as to what these boundaries are, with different militias holding various beliefs as to which laws or actions violate the Constitution.
One common belief among groups in the militia movement is that they must organize to defend the Constitution against what they refer to as the New World Order. These militias believe that this is an international conspiracy that has taken over most governments of the world, and deprived those citizens of their rights and liberties. Militia members attracted to this idea believe that this conspiracy is in the process of trying to take over the United States, and that they must train to fight the conspiracy's soldiers when they inevitably attack.
Some particularly religious militias believe that the attack of the New World Order will coincide with the coming of the apocalypse. Each of these groups tends to form around the ideas of an individual who claims to have had a special spiritual revelation. Religiously-motivated militias differ in their exact beliefs and goals because these form around the varied ideas and philosophies of different individuals.
Racism is another idea around which some militias form. Such groups hold the belief that the American government is being led away from its constitutional basis by non-white citizens. These people often justify acts of violence against minorities as defending the ideas behind the Constitution.
Groups within the militia movement are not necessarily violent. Some militias focus on holding public forums to discuss libertarian political philosophy. Others create or provoke conflicts with law enforcement agencies when they plan acts of violence or stockpile illegal weapons.