In Somalia, hard-line Islamist fighters are trying to overthrow a weakened central government, and the ongoing fighting between militants and government forces has forced millions to flee their homes.
In addition, drought conditions that have persisted for more than five years have made life difficult for farmers and others even in quiet areas.
Pakistan also is suffering from large-scale displacement due to the government efforts to conquer Taliban strongholds, aid agencies say.
Exacerbating the problems in these and other areas is the difficulty organizations say they face when trying to reach trouble zones, including security problems and uncooperative governments.
Representatives of three international aid groups describe what they consider the most severe humanitarian crises of 2009:
Acting president of Refugees International
"In [Somalia,] a country of 9 million people, you have 3 million ... displaced largely due to conflict, but now also due to drought. You just have a perfect storm in Somalia of factors that makes it very difficult for people to survive," he said.
Charny outlines Somalia's troubles here:
Senior vice president of the International Crisis Group
"As you go beyond the emergency relief phase [in Pakistan], you need to have a comprehensive development strategy that engages the individuals themselves, their communities, as well as the range of governmental agencies to prepare an integrated strategy for the return of these individuals," he said.
Schneider describes more here:
Dr. Matthew Spitzer
President of the board of directors of Doctors Without Borders-USA
"We think about it really as two main trends or two main challenges that have really come to the forefront. The first of these is issues with either blockage or obstruction of actually assisting the populations we work with. ... Another thing is medical neglect," he said.
Hear more of Spitzer's answer: