Thing is, what you describe ("Merely installing a peacekeeping force, and then concentrating on the reconstruction of those countries -- the building of schools and hospitals, and other infrastructure") is precisely what did happen in the DR Congo and Sudan. In both cases the United Nations and African Union deployed a large peacekeeping force of approximately 16 000 troops in each country, armed in some cases with AFVs and attack helicopters, and backed them up with a significant civil assistance and reconstruction program. All this was funded largely by the US and EU, the UN's primary donors.

In neither case was the peacekeeping mission itself particularly successful. MONUC in the DRC stood impressive but ineffectual for over a decade as the violence continued raging around them and civilians continued dying and being terrorised. The violence has arguably died down only because President Kabila has proven to be fairly tenacious and the government army has managed to restore some level control in certain areas, thanks in part to training by Belgian and South African military advisors. UNAMID in Sudan did not seem to achieve much, though their reporting was valuable, with much of the progress in that country seemingly being due to the ongoing strengthening of the South Sudanese rebel movements and the severe international pressure that worked for once. In retrospect, we may be able to claim that both missions were ultimately successful, but it's clear that if it's a rapid end to violence and an improvement in basic human security you want then look elsewhere.

These conflicts are usually just too much of an intractable problem for peacekeeping to be of any real effect. For one, peacekeeping by its very nature tends to preserve the status quo, by slowing the conflict down and preventing either side from gaining a swift advantage, but this is what allows these conflicts to drag on for decades without any real winner. For another, peacekeeping forces are seldom capable of performing offensive missions to wipe out rebel forces and their leaders or groups of bandits, not only because they're not funded for it but because that would require deciding from the outset who to support and who to destroy and the UN, in order not to adversely effect possible negotiations, usually tries to avoid that. After all, what if you make the wrong choice? Finally, how do you build a state up without any kind of central authority around which to hang the authority, monopoly of force and institutions needed to ensure human security? This by the way was a large part of the problem in Iraq, where the US had to create a central authority from scratch and found it to be a whole lot harder than initially thought.

If you are willing to make a snap judgement about who is 'good or bad' in a conflict though, there are solutions that will result in short-term stabilisation. One of these is the use of mercenaries, who have proven in the past (see Executive Outcomes in Sierra Leone and their proposed intervention plan for Rwanda) to be effective in this sort of scenario. However, the use of mercenaries is undoubtedly subject to abuses and it's a short-term solution in most cases, as the core civil and social dysfunction that permitted the breakdown in order in the first place remains present. However, they also only work best in cases where they're able to piggy-back off some sort of central authority and where they have a clear mandate and a clear distinction of who the good and bad guys are. And when they leave, as when Executive Outcomes left Sierra Leone to be replaced by a UN peacekeeping force, the violence can start up all over again.

In the end I think the sad fact of the matter is that this is not a simple problem to solve, despite surface impressions. Conflict, crime, poverty and sexual abuse in many African countries is all part of the same issue, of states and civil institutions that are either totally dysfunctional or entirely non-existent, a concurrent tendency for regions to produce warlords rather than self-sufficient federalist enclaves and the immense difficulty both the people living in the country and those from outside face in trying to build a viable and secure system of governance in a place that has little or nothing on which to build. So unfortunately, I think we're going to be living with this problem for a long time to come.