A  leaked report  written by the Missouri Information Analysis Center (MIAC) and  dated February 2009 provides background on the modern militia movement.  I suspect rank and file militia members are fearful people who do not have any confidence in themselves and who are easily led by people who want to hold power over other.  That being said I'll take my amateur shrink hat off now and let you come to your own conclusions. 

I have summarized part of the report below, but recommend you read the entire 7 pages if the subject concerns you. It fleshes out the bulleted information provided here. 

The militia movement began in the 1980s and reached its peak in 1996. 

1980s

Factors contributing to the movements:

• Loss of over 11 million jobs
• Loss of 75% of small and medium family farms
• Gains by women and minorities in the 60s and 70s probably hurt white male egos
• Increased immigration and loss of employment
• Sense of defeat in Vietnam
• Rise of paramilitary culture

Conspiracy theories arose at the center of which was the fear of a New World Order (NWO), a global government which would exploit working men ; UN troops were thought to be in the U.S. in support of the NWO.  Many of the groups were anti-Semitic believing that Jews controlled the monetary system and the entertainment industry.

1990s

Factors contributing to the movements:

• Ruby Ridge standoff
• Branch Davidian standoff
• Brady Bill

The movement did not disappear in the 2000s, but apparently it was less active.  The movement is reemerging now because of high unemployment, the cost of living, and the election of the first African American president. (Personally, I suspect President Obama's election is the primary factor)

Additional factors feeding the movement:

• Ammunition Accountability Act
• Anticipation of the economic collapse of the U.S. government  (They are disturbed by Igor Panarin's view  of what happens to the U.S.  following the collapse)  Heads up Quinn!  Canada gets a big chunk.
• Possible Constitutional Conventions (Con Con)
• North American Union/NAFTA highway
• Fear of Universal Service program
• Radio Frequency Identification (RFID )

Militia member  see themselves as:

• Christian
• White nationalists
•  Sovereign Citizens
• Militantly anti-abortionist
• Tax resistors

The Missouri  report continues with notes about their training, organization, and symbols.   Some on the right are claiming the report smears Ron Paul, people who display bumper stickers, own gold... so on and so forth, ad nauseum.