benign geography

You need to provide us some context. Can you quote the passage in which you have read it? This is not a stock phrase in English, so no one will be able to answer your question without seeing the context.

the context is :
The United States has been able to overcome its challenges by a combination of idealism,willpower,organization and benign geography.

OK, what the phrase means here is that the geography of the United States has contributed to it's success. I don't know what the author means by challenges, because, basically, the United States has been one of the luckiest nations in history.

The land within the United States is comprised of vast amounts very fertile farm land, good grazing land, mineral deposits (for mining), lots of rivers (for transporting people and goods)--and it is located in the temperate zone, which is also good for farming. The United States has been, primarily, an agricultural nation for all of its history, and that's a good thing--it helps to support a large population, which helps industrialization, too.

And that's what the author means by benign geography.

some meanings of benign are Kindly, showing gentlness, pleasant, favorable, beneficial.
substituting any of these for beign in the passage will meet the authors intention

thanks for your answer!

The meaning of the "benign (kind) geography" of the United States is that its size, position on the globe, geology, mineral resources, climate etc are favourable.