These are easy to find and contain reliable, quality resources. When searching full text, you must use the words of the TIME. For example, you cannot search WWI if looking for newspapers from that time - it was not called WWI until WWII happened! You'll have to try things like "Great War" or even just search "war" and use the time period limiters on the side.
There are too many open digital collections to include here; this is just a sample of what is out there! if you find a collection online, please check with your librarian or Dr. Kawamura to make sure that it is reliable and good for your topic. Here are a few larger collections; you can do searches within these to find more specific sources. Try to Google the name of the war and "digital collections" - and look for those housed at universities, libraries, or government and cultural institutions (not just some random blog or website!).