How to Take Over the World

Short Description:  This is the oldest way; you build a gi-freakin'-gantic military force and defeat everybody who would stand in your way.

Up-front Preparation:  You'd need to build a military bigger (or at least better) than that of the rest of the world militaries.  Since military spending is one of the biggest expenses of the world governments, this is BIG money.  You'd also need to somehow make sure that your commanders remain loyal to you and don't just betray you and set up their own feifdoms.

Timeframe:  If you're strong enough, taking out the major military forces would take a few years.

Potential Resistance:  This is the big problem.  This type of conquest would drive guerilla forces into every backwoods area of the world.  Subduing them all could take decades or possibly even centuries.

Real Examples:  Every conquerer in history has tried this from Alexander the Great to Julius Caesar and Genghis Khan (and those are just the reasonably successful ones).  This has been seriously tried hundreds of time in world history.

Fictional Examples:  This has been done time and again in fiction.  It's a classic.

Escape Plan:  How bad failure is depends on whether your techniques are nasty enough (genocide, nukes, etc.) to unite the rest of the world in a single force to defeat you or not.  If you're lucky you'll merely end up controlling a large empire.  If not, well, they kill failed tyrants.  Sometimes quite painfully.

Drawbacks:  The battles will do some damage to people and property, depending on how much damage you feel you need to do in your conquest.  Then again, the world has been damaged that way constantly through history, so it might not be that much worse than normal.