I'll give short answers - detailed analyses citations will be provided to repair your ignorance on the subject upon request.
Great Depression: The federal reserve, a progressive idea, was created in 1913. It greatly expanded credit in the 1920s with cheap money, causing a huge credit bubble which finally collapsed. Herbert Hoover, whom I'm guessing you don't know created a number of the seminal programs of the New Deal, signed the smoot-hawley tariff law, putting the last nail in the coffin.
S&L: The tax reform act of 1986 created by the democrat congress sank the values of real estate holdings, creating a real estate bust. This immediately put S&L's whose main business is real estate, in a critical financial condition. Further, because of prevailing high interest rates, S&Ls continued to invest in risky real estate projects, because they could then pay depositors the high rates investors could command, since there were other investments offering high rates. Investors would only put their money in such S&Ls because they were backed by the FSLIC (government market distortion) otherwise no sane person would have given them a dime, and they would have collapsed without taking many people with them.
2008 Collapse: Starting in the 1970s, under Carter, the Community Reinvestment Act was passed, in effect requiring banks to make home loans to unqualified minority constituencies of the democrat party. This had a small effect, until it was vastly ramped up under bill clinton, who appointed franklin raines head of fanny mae, with marching orders to offer a secondary market for huge numbers of such loans. With fanny mae and freddy mac doing a landslide business in such loans, investment banks were encouraged to join in. Members of the Bush administration began to see the danger and approached Barney Frank, democrat head of the house banking committee, to rein in fanny mae - Frank brushed them off.
In every case, it was government meddling in markets that otherwise would have quickly self-corrected without disaster.
Not what you heard on msnbc and cnn, huh?
It's funny - every time government creates these disasters, they say "duh...it was capitalism what done it". They do so because they know the country is loaded with legions of uninformed morons who will lap it up.