"of or pertaining to a nation or a country regarded as a whole; established and maintained by the nation; peculiar to the whole people of a country," 1590s, from French national (16c., from Old French nacion), and also from nation + -al (1). Opposed to local or provincial (or in the U.S., state).

Meaning "peculiar or common to the whole people of a country" is by 1620s. From 1802 as "established and maintained by the nation or its laws." As a noun, "citizen of a (particular) nation," from 1887. Related: Nationally. 

National guard is from 1793, originally in reference to an armed force in France identified with the revolution; U.S. use is from 1847, originally a name sometimes given to the organized militia. National anthem is recorded by 1806. 

A King though he's pestered with cares,

    For the most part he's able to ban them;

But one comes in a shape he never can escape—

    The implacable National Anthem!

[W.S. Gilbert, "His Excellency," 1894] 

late 14c., "deadly, destructive to life; causing or threatening death" (of illness, poisons, wounds, etc.); also, of persons or the body, "doomed to die, subject to death;" from Old French mortel "destined to die; deserving of death" and directly from Latin mortalis "subject to death, mortal, of a mortal, human," from mors (genitive mortis) "death."

This is reconstructed to be from PIE *mr-o- "to die," *mr-to- "dead," *mr-ti- "death," all from PIE root *mer- "to rub away, harm" (also "to die" and forming words referring to death and to beings subject to death). The most widespread Indo-European root for "to die," it forms the common word for it except in Greek and Germanic.

"Subject to death," hence "human, of or pertaining to humans" (early 15c.). Also from late 14c. as "implacable, to be satisfied only by death" (of hatreds, enemies, etc.). Meaning "extreme, very great" is from late 14c. A mortal sin (early 15c., opposed to venial) is one that incurs the penalty of spiritual death.