country
国 centers on a defined territory with its own identity: a country or nation. The meaning is straightforward and concrete.
country; state
China
South Korea; Republic of Korea
the whole country
within the country; inside the county; domestic; home; internal
people (of a country); nation; citizen; national
state; country; nation
international
foreign country
(United States of) America; USA; US
National Diet; legislative assembly of Japan (1947-)
empire
kingdom; monarchy
national; founded and run by the central government
United Kingdom; Britain; Great Britain
paradise; heaven; Kingdom of Heaven
border (between countries); national border
country in civil war; country disarrayed by war
nationality; citizenship
each country; every country; various countries; all countries
United Nations; UN
king; queen; monarch; sovereign
return to one's country
Shikoku (smallest of the four main islands of Japan)
国 is the modern simplified form of 國. The older form combines 囗 (enclosure) with 或, which likely contributed the sound and the idea of a territory. The modern form replaces the inner part with 玉 (jewel), a simplification that does not reflect the original component.
The enclosure 囗 represents borders, and inside is 玉 (jewel). Picture a country as a precious jewel protected within its borders.
For コク, imagine a country shaped like a coke bottle: coke -> コク, and the bottle's outline forms the borders of the nation.