Oversimplification

You oversimplify when you cover up relevant complexities or make a complicated problem appear to be too much simpler than it really is.

Example:

President Bush wants our country to trade with Fidel Castro's Communist Cuba. I say there should be a trade embargo against Cuba. The issue in our election is Cuban trade, and if you are against it, then you should vote for me for president.

Whom to vote for should be decided by considering quite a number of issues in addition to Cuban trade. When an oversimplification results in falsely implying that a minor causal factor is the major one, then the reasoning also commits the false cause fallacy.