While South Asian nations (especially Pakistan, India, and Bangladesh) are most frequently seen operating as UN peacekeepers, and these three nations are indeed among the largest contributors of peacekeepers, there is another nation that is also a major contributor that rarely gets mentioned. That is Nigeria, which since 1960 has sent over 250,000 of its troops on UN peacekeeping missions. Nigeria has spent about $13 billion on that peacekeeping effort and been compensated for that, and then some, by the UN (using mostly money contributed by Western nations, who provide most of the cash that keeps the UN going). Nigeria is one of the few African countries able and willing to supply peacekeeping troops.
Currently about a third of the UN peacekeepers on duty come from nations that were formerly part of the British Empire (mostly from what used to be British India, which includes India, Pakistan, Bangladesh and Nepal, as well as Nigeria.) To maintain and protect is empire, the British recruited lots of local troops and trained them as they would British soldiers. While most of the officers were British, most of the NCOs were locals. Before the British relinquished its colonies after World War II, it also trained many locals as officers. Much of this Western training and military traditions took hold, especially in South Asia and the African nations that were British colonies. Britain also raised many troops in South Asia and Africa during World War II, and these men served as the leaders and trainers of the military after these nations became independent after World War II (from 1947 to the 1960s).
The British encountered some formidable local armies when they moved into India in the 18th century and Africa in the 19th. But the British had better technology and more advanced military doctrine. The Indians noted this, and some of the local rulers quickly, but not quickly enough, adopted the superior British practices. When the British left, the South Asian and African armies remained very British in the way they trained and operated. That meant well trained and well led troops but without all the gadgets that Western nations lavish on their soldiers. For peacekeeping operations, the disciplined and reliable South Asian and African soldiers are excellent. Those troops from other less affluent nations often lack the discipline and good leadership and account for most of the peacekeeping scandals.
Meanwhile, corruption, casualties and lack of success are discouraging countries from contributing their troops for peacekeeping. The corruption angle is interesting, as it pertains both to the corruption within the UN bureaucracy and the corrupt atmosphere the peacekeepers operate in and often succumb to. Casualties are expected, but the contributing countries feel a lot of their troop losses are the result of restrictive UN rules that limit what peacekeepers can do. This, in turn, is believed most responsible for a lack of success for many peacekeeping missions.
India, Bangladesh, and Pakistan (who contribute nearly a quarter of the UN force) are also not happy with the lack of volunteers from other major nations. The chief reasons for that are the same ones annoying the current peacekeepers (corruption and restrictive rules of engagement). In addition, the major military powers (with the exception of China and Russia) feel they already contribute quite a lot in the form of money to pay the peacekeepers. And the contributors are also upset at the lack of results.
Currently the UN is spending about $7.5 billion a year to keep about 100,000 peacekeepers in service. For the last decade annual peacekeeping spending and the number of peacekeepers in action has remained pretty much the same. It's actually a pretty cheap way of keeping some conflicts under control. The causes of the unrest may not be resolved by peacekeepers but at least the problem is contained and doesn't bother the rest of the world too much. This is an increasingly unpopular approach to peacekeeping, except in the UN bureaucracy. Many UN members would rather send peacekeepers to where they are not wanted (by the government, usually a bad one that is often the cause of the trouble in the first place) and prefer to emphasize keeping peacekeeper casualties down and the situation quiet.
Most of the money is going to a few large peacekeeping operations. Three of the largest (Congo, Darfur, and south Sudan) get over half the cash. Africa has the largest number of "failed states" on the planet and, as such, is most in need of outside security assistance. The Middle East is also a source of much unrest. But there the problem isn't a lack of government, just bad government. Most Middle Eastern nations are run by tyrants, who have created police states that at least keep anarchy at bay.
It’s not just the money that encourages nations to offer their troops for peacekeeping duty. There’s also the fact that casualties are pretty low but the troops are still exposed to some combat and the kind of stress you only encounter in a combat zone. This is considered excellent training. The UN's peacekeeping army suffers less than a hundred combat deaths a year. More than ten times that number were wounded, injured in accidents, or disabled by disease. The peacekeeper combat fatalities come out to 90-110 per 100,000 troops per year. In Afghanistan foreign troops lost about 350-450 in 2012. At the peak of the fighting (2005-7) in Iraq, the losses were 500-600 per 100,000. The rate for U.S. troops in Vietnam and World War II was about 1,500 per 100,000 troops. So the UN peacekeepers are often seeing some considerable violence but at less than a third of the rate of troops in actual wars. The Pakistani experience has been typical. Pakistan has sent 145,000 troops to 41 UN peacekeeping operations in 23 countries over the last half century. They suffered a death rate of 92 per 100,000. That’s lower than usual for peacekeepers, in large part because the South Asian troops tend to be among the best trained and most professional in the UN force and best able to take care of themselves.