You won't save shit. The population will hate you and you'll constantly have to fight a brutal and bloody insurgency war, like what's going on in Iraq and Afghanistan. The only advancement that will come is that you'll unite the country for a short while against a common enemy. Once you give up in frustration and leave, they'll go back to raping and killing each other.
The fact of the matter is, Africa and much of the Middle East is so fucked up (largely because they do it to themselves), it's going to take centuries of cultural and political change before they can get past the feudal era. Nothing we (as in the West) can do is going to speed up that process. Latin America is a little better, but their problem is socialist/fascist government, which again we can't fix for them.
As a matter of comparison, it took England roughly 100 years to go from feudal monarchy to parliamentary democracy. The UK was at that time the world's superpower, with massive gold reserves and a navy (sea power was the trump card of that era) that few if any could match (think America today, minus the world-wide empire). So, if it took England that long to transition (and they had their fair share of wars and political/religious purges during that period), expecting the Third World to do so in our lifetime is ludicrous. They don't have anywhere near the same resources, education or political stability.
My personal feeling is that we should just let things progress normally. Some Third World countries have already begun modernising and stabilising politically, and are trading/sending their kids overseas to be educated in the West. Others continue to be hellholes, others are just stagnant and corrupt. In any case, countries are going to have to fail or succeed on their own merits. Outside influence generally just makes things worse.
If you wanna be really extreme, you could just nuke the whole lot. Socio-political problems don't matter if all the participants are radioactive ash. Wait a few centuries, go in with clean-up crews, re-populate.