The brave men living and dead who struggled here have consecrated it far above your poor power to add or detract?

It is struggled here. This is a quotation from Abraham Lincoln's Gettysburg Address. If you attend school in the United States, you will probably memorize it sometime.

This sentence refers to the men who fought on the battlefield during the Battle of Gettysburg at Gettysburg, Pennsylvania. It says that the battlefield was made holy by the men who fought there and not by a group of speakers talking about the the battle long afterward.

The significance of the battle was that the Union Army defeated Lee's Confederate Army.

The significance of the speech was that the first sentence changed the purpose of the war from preserving the Union to freeing the slaves. The last sentence made the nation a democracy and made the purpose of the war an effort to prevent its unraveling.