The first example I think of would be the aid given to South Korea. While communist forces were never pushed out of NK, SK was kept intact. And while it certainly didn't have a spotless history for years after the war, the fact that it was allowed to be separate from NK allowed it to turn into the well developed country it is today.

The important thing to remember when thinking about things like the wars in the mid east is that it takes a very long time for a country to develop into something successful. South Korea was given an opportunity, and decades later became great. You shouldn't judge more modern "nation building" too harshly, as we can never be sure what effect something so major can have for many years.

I know this example is before your desired 1950's date, but the US revolution is another important example. And it isn't much different from similar wars since the 1950s. The French aided the rebelling colonies greatly. Foreign military aid has even been a strategy for some rebels, since it is often the only way for an inferior force to win. During the American Civil War, for instance, the South was hoping to last long enough to get aid from across the Atlantic.

This can work, but often requires aid of different types for a long time after any war was won. You also need to make sure a proper government is in place. Military aid is only step one and, arguably, the easiest step.