Hello. You did not submit the text to which this question refers, which makes it impossible for this question to be answered. However, I will try to help you as best I can.
A textual evidence is a statement that proves an argument or information presented by the author of a text. This statement explains why the information in the text is correct, how events presented in the text happened and even confirm facts and justify ideas presented in the text. In this case, to answer your question, you will have to read all the text that is related to it and identify the sentences that try to explain and show how the territorial expansion in 1840 happened. This evidence can be considered good and effective, if it presents historically proven justifications for territorial expansion, going so far as to prove to the reader that this expansion, in fact, happened, and presenting the reasons that established it.
