Political Battlegrounds

Elections are not properly fought with muskets and cannon, but figuratively speaking, any area where there is a fierce political campaign, with the final outcome in serious doubt, can be referred to as a political battleground.

(Above: Depiction of the Battle of Gettysburg)

Example: Last week the U.S. Chamber of Commerce pumped more than $10 million into key battlegrounds.

Here, "key" just means crucial, and provides emphasis to the battleground part, indicating that this political advertising went into areas with highly competitive political races where such advertising could alter the final outcome.

This and the preceding three posts were inspired by this article: http://news.yahoo.com/s/ap/20101012/ap_on_go_pr_wh/us_chamber_of_commerce_obama_1

I only altered text for educational purposes, as quoting certain parts without the full context required adding details ("the chamber" -> "the U.S. Chamber of Commerce"), and quoting large portions at one time would have been too confusing to non-native learners.