Thomas Jefferson concluded the Louisiana Purchase which totalled 828,800 square miles.
The Mexican Cession was 525.000 square miles, but if the land that Texas claimed is added in, it totals about 1.2 million square miles and was concluded under James K. Polk.
Andrew Johnson picked up a mere 663,268 square miles with the purchase of Alaska.
William McKinley's acquired Puerto Rico (3,515 square miles), Hawaii (10.931 square miles), Guam (209 square miles) and the Philippines (115,831 square miles) for a total of 130,486 square miles which is hardly a drop in the bucket.
Jefferson got the best deal by far because like the purchase of Alaska no lives were squandered in warfare and no Army had to be equipped and paid for to achieve the National goal and neither were seen as acts of American Imperialism by the World in general.
Chat with our AI personalities
France felt its interests in the Caribbean were most important.
California,Nevada, Utah,most of Arizona,and parts of New Mexico, Colorado,Wyoming and Texas!
The Qing Dynasty controlled the most territory in China.
Most did not, and those like Secretary of State Seward and President Johnson could not find solid arguments that would support Alaska's Purchase. For most it was just an after thought and the real prize was getting Russia out of the New World and clearing any Russian claims to Oregon Territory.
The importance of territory is that it clearly defines an area and can eventually be considered as a state. Most territories that are ungoverned are a main source of conflict for powers who intend to take them under their governments.