If you could focus all of the money and effort that people donate to advance causes to a single end, what would you pick?

There are hundreds, possibly thousands of causes out there, all with a yen for your dollar. These operate on the assumption that more money/time/effort sent their way will further the cause and ultimately accomplish the goal.

Think torrents.

Naturally, splitting up the disposable portion of a nation’s income a million ways is slow going. Presumably, focusing the bulk of those resources on one cause at a time would get one to the individual goals more quickly.
Question is, which would you focus on first?