It means to keep stay united. A good example of this was the American War Between the States also known as the Civil War. The war was fought to keep the states united into one country instead of two separate countries.
Lincoln declared war in order to preserve the Union, and the Northern armies were raised for this purpose.It was not for another eighteen months that he changed the war-aims into an official crusade...
Declared war on the Confederacy.Took illegal steps to keep four of the slave-states loyal.Issued the Emancipation Proclamation, chiefly to keep the British from helping the Confederates.Learned to...
By putting pressure on the slave-states of Missouri, Kentucky and Maryland to stay loyal, or at least neutral.By keeping Britain and France out of it, when he eventually declared it to be a war...