Where can i get some critics on Carl Sandburg's work and how he carries the theme of war, bloodshed throughout all his poetry?
Perhaps the best place to turn for literary criticism would be a library's electronic database or two, such as the MLA International Bibliography or Academic Search Premier. In searching a database, you can enter not only the poet's name but also a keyword or two, such as "theme" or "war." The results can sometimes be accessed on the spot, depending on the library's holdings and subscriptions.
A simple Google search won't generally net you the same level of results, but you won't usually have to wait to get the information (such as through interlibrary loan).
If you really can't get to a library and need a quick answer, sometimes a search in Google Books (a service accessed through Google; see the "more" button along the top of the search page) will lead you to published materials that you can read online. These materials are often searchable and sometimes are as long as entire sample chapters from a book. You usually won't be able to read very much, though, and having access to the full book (e.g. through a library) is always better.
Having said all that, I have looked and haven't found much on Sandburg's treatment of the theme of war. You may want to follow the first link below, to a listing of enotes resources. Maybe some fo those items will be available and helpful to you.
Some good enotes links added below: