Websites provides free and open source sites provided by government agencies and nonprofit organizations. These sites are useuful for obtaining brief overviews of the theme you are studying.

The National Archives and Records Administration provides a vast array of links to various government documents and websites relating to the Vietnam War.

The Lehrman Institute is a nonprofit organization that provides excellent timeline histories by era. The era, 1945 to the Present, provides sub-era histories on Postwar Politics and the Origins of the Cold War, 1950s, 1960s, and Civil Rights Movement

This office provides Milestones in the History of U.S. Foreign Relations, a general overview of the history of U.S. engagement with the world through short essays on important moments, or milestones, in the diplomatic history of the United States. The years from 1941 are particularly relevant, particularly as it relates to the Cold War,

The Civil Rights Era, is explored in The Library of Congress exhibition, The African American Odyssey: A Quest for Full Citizenship, which covers black America's quest for equality from the early national period through the twentieth century.

The Cold War Museum is a highly useful and credible site with a detailed timeline on all the key moments in the Cold War, notably with essays on the Berlin Blockade, formation of NATO, the Marshall Plan, U-2 Overlights, Cuban Revolution, and so on.   This is a useful site to get started with your research.

These are some of the websites focusing on World War II's history which are excellent resources to find overviews to start your research project.