This list focuses on databases that emphasize colonialism. There are many other options for primary sources, especially British and American. Please see my British and Irish History Research Guide and United States History Research Guide for those lists, or ask me.
Use the Library Catalog to find books. Be sure to pay attention to the date and publisher of the book - the Catalog does include older materials and primary sources.
Use these databases to find articles from scholarly journals. Scholarly journals also have features like book reviews, so make sure it's a research article.