United States politics
United States Politics is the rubric under which the American people attempt to control their country. The political system in the US has favored a two party system (currently Democrats and Republicans) that is more or less "Liberal" and "Conservative", though how true those terms would apply changes in any given generation.
Unlike European and UK political systems where any of a rather large collection of parties, representing a true diversity of ideas and ranges of political spectrum, the US system allows for only two viable parties that are fundamentally similar on most political issues when compared to a world political spectrum.
While it is easy to "take sides" in a two party system, it does mean that no real change is likely to happen, since it is next to impossible for a third-party candidate to win any major state or national position. There have been some third party candidates who have "affected" national elections, but their effect is generally to split the vote of one of the two parties, letting the other party win almost "by default".
The two party system has recently devolved into 5 year olds having playground battles over who is rubber and who is glue.
Outside of its own borders, the United States has a long and storied history of involving itself in just about every situation and believing that picking the worst possible allies is preferable to not getting involved.
 Democratic Party
The "liberal" party. Actually it's a centrist party that leans to the right or left depending on the time of day (today, it's typically to the right). Despite being denounced as commies by the GOP they would be considered fairly conservative by international standards, only being consistently liberal on certain social issues (LGBT rights being the main such issue of today) and immigration.
 Republican Party
The "conservative" party. Actually, it's more radically right wing than conservative, with a current platform that includes hardcore social conservatism, Nationalism-lite, hawkishness overseas, laissez-faire economics, support for austerity taken to cranky levels, and "fiscal conservatism" (unless they're in power – then they blow everyone's money on certain projects).
 Current leadership
Simply put, it's the almighty dollar. If you don't have the financial support of the businesses that own Washington, you may as well not bother running; no one will ever know you're there. Parties outside the two-party system, such as the Libertarian Party, tend to get very few votes by comparison.
- I Hate Your Politics, John Scalzi