London, England (CNN) -- Over the last two decades the humanitarian organization International Medical Corps has cared for hundreds of thousands of victims of wars and natural disasters in more than 25 countries.
From the genocide in Rwanda to the the 2005 earthquake in Pakistan and Hurricane Katrina, the International Medical Corps (IMC), has witnessed first hand the devastating impact of each tragedy.
IMC recently released a book titled: "A Thousand Words: Photos from the Field," which chronicles the organization's 25-year history.
CEO Nancy Aossey told CNN, in an exclusive interview, the stories behind some of the most powerful and dramatic images, spanning more than 20 years.
"I have witnessed some of our generation's worst human tragedies -- and the remarkable resilience of the human spirit," said Aossey.
"Each photograph in this book is a profound reminder of the incredible journey of International Medical Corps, and the exceptional efforts of our colleagues who have cared for hundreds of millions of people in these fragile, often dangerous environments."
Aossey was in Rwanda in 1994, when approximately 800,000 minority Tutsis and moderate Hutus were murdered. "Rwanda was unlike anything I had ever seen," Aossey said.
"The scale, the swiftness and the brutality of the killing was staggering and bodies were piled up everywhere. Most of the organizations were providing services in the refugee camps on the border but we stayed inside Rwanda."
International Medical Corps is also present when natural disasters strike. After the 2004 tsunami in Southeast Asia, the California-based agency was one of the first organizations on the ground.
One of the problems it dealt with was mental illness. "After the tsunami we were involved with children who had post-traumatic stress, but also mental illness. So often, in these natural disasters or conflicts, people with mental illness have an especially difficult time," Aossey said.
International Medical Corps was founded in 1984 by American Dr. Robert Simon, who wanted to take action after seeing the tragic situation of the Afghan people following the 1979 Soviet invasion. According to IMC, only 200 of the country's 1,500 doctors remained alive and all relief agencies had been forced to leave the country, meaning civilians in need of basic health care had nowhere to go.
Dr. Simon therefore set up an Afghan medical training center in neighboring Pakistan. At the end of their training, "our Afghan medics could diagnose and treat 75 to 80 per cent of the injuries and illnesses they encountered in the field," IMC said.
Over the next two decades, IMC provided medical help in over 45 countries and was present at some of the most devastating man-made and natural disasters, including the famine in Somalia, ethnic cleansing in Bosnia, atrocities against children in Sierra Leone.
It is also one of few humanitarian agencies still working in Darfur and Iraq today.