These "similar" organizations are not quite similar at all.
As regards the Peace Corps, this is a category unto itself and is far from the likes of the American Red Cross. The Peace Corps may be exposed to potentially hazardous environs and bear commitments somewhat remnant of the armed forces -- but, then, they are dissimilar to the armed forces, too, in that theirs centers on peace and not war. It is a salaried organization -- but scarcely are these well-salaried positions -- that falls under the umbrella of the U.S. federal government, and which workers toil in all manner of environments and cultures around the world, working in close quarters with people to help re-constitute cultural circumstances caused by events that result from natural disaster, war, poor economic practices, and other unforeseen phenomena.
The American Red Cross is exclusively volunteer, with only the smallest of percentage paid employees, but the bulk of the ARC is volunteer, to which the inroads for employment are best availed through performing volunteer work first. Because it is one of the oldest organizations, going back to the American Civil War, founded by Clara Barton, it bears certain traditions that are somewhat anachronistic and is 'very' conservative. That is, there is somewhat impression that the volunteer has first to pass the "Good Housekeeping Seal of Approval" before one can proceed into mission-level managerial positions. One who has or who wants to get experience in Emergency Management is among their top priorities, and one may may work locally or nationally or even internationally, on set or stand-by schedules. Training is on-going, and many of these workshops are free to the volunteer who works for the ARC, who would otherwise pay for that training.
Amnesty focuses on Human Rights and is, say, politically oriented in its objectives and mission. One whose concentration in Law, Sociology, Philosophy, Economics, Public Policy, Public Health and generally the social sciences would be strong points for this organization. Amnesty is of among the rabble rousers, which fosters awareness and justice and ethics, and human and civil rights around the world.
These organizations do not bear the traditional corporate ethos, partially because theirs are essentially volunteer-based and thus pay little if anything compared to what a traditional corporate venue would pay. Generally, the degree itself tends to be the door-opener and not necessarily is there a specific type of degree required, though in each organization there can be a preference for one type of degree over another.
Since there exists hundreds of these organizations, local, national, international, you just have to find what suits your temperament and interests best, then work from that point, and be sure that you can afford the time to give. For again, these generally are 'not' paid positions except for a few executive managerial level positions needed to run their programs and ventures.
Answered By: path less travelled - 12/26/2009