Refers to a theory developed and popularized in the 19th century to provide a rationale for the united states to expand from the atlantic ocean to the pacific ocean.

theodore roosevelt 26th u.s. president : i admire his energy and passion. he was a fundamentally good man, brilliantly intelligent, possessed of extraordinary will and ability, supremely self-confident, bold, egalitarian, idealistic…. , lord, can we have him back?

use wikipedia, i think they have this.