Just as Hadrian succeeded Trajan, Domitian succeeded Titus, Nero succeeded Claudius, and Caligula succeeded Tiberius, so Kennedy replaced Eisenhower, Nixon replaced Johnson, Reagan replaced Carter, and Obama replaced Bush.
Same empire, different emperor.
The extent of the U.S. global empire is almost incalculable. We know enough, however, about foreign bases, physical assets, military spending, and foreign troop levels to know that we have an empire in everything but the name.
There are, according to the Department of Defense's "Base Structure Report" for FY 2009, 716 U.S. military bases on foreign soil in thirty-eight countries. Yet, according to the expert on this subject, Chalmers Johnson, the author of Blowback, The Sorrows of Empire, and Nemesis, that number is far too low: "The official figures omit espionage bases, those located in war zones, including Iraq and Afghanistan, and miscellaneous facilities in places considered too sensitive to discuss or which the Pentagon for its own reasons chooses to exclude -- e.g. in Israel, Kosovo, or Jordan." Johnson places the real number of foreign bases closer to 1,000.
This same Base Structure Report states that the DOD's physical assets consist of "more than 539,000 facilities (buildings, structures and linear structures) located on more than 5,570 sites, on approximately 29 million acres." The 307,295 buildings occupied by the DOD comprise over 2.1 billion square feet. The DOD manages almost 30 million acres of land worldwide.