infest (v.)

late 14c., "clearly revealed to the eye or the understanding, open to view or comprehension," from Old French manifest "evident, palpable," (12c.), or directly from Latin manifestus "plainly apprehensible, clear, apparent, evident;" of offenses, "proved by direct evidence;" of offenders, "caught in the act," probably from manus "hand" (from PIE root *man- (2) "hand") + -festus, which apparently is identical to the second element of infest.

De Vaan writes, "If manifestus may be interpreted as 'caught by hand', the meanings seem to point to 'grabbing' or 'attacking' for -festus." But he finds none of the proposed ulterior connections compelling, and concludes that, regarding infestus and manifestus, "maybe the two must be separated." If not, the sense development might be from "caught by hand" to "in hand, palpable." 

Manifest destiny, "that which clearly appears destined to come to pass; a future state, condition, or event which can be foreseen with certainty, or is regarded as inevitable" was much used in American politics from about the time of the Mexican War "by those who believed that the United States were destined in time to occupy the entire continent" [Century Dictionary].

Other nations have tried to check ... the fulfillment of our manifest destiny to overspread the Continent allotted by Providence for the free development of our yearly multiplying millions. [John O'Sullivan (1813-1895), "U.S. Magazine & Democratic Review," July 1845]

The phrase apparently is O'Sullivan's coinage; the notion is as old as the republic.

early 15c., "a being infested," from Old French infestacion, from Late Latin infestationem (nominative infestatio) "a troubling, a disturbing, a molesting," noun of action from past participle stem of Latin infestare "to attack, disturb" (see infest).

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.