Several parts combine into one character.

The country-character has TWO scripts to learn: — Traditional 繁體 國: an enclosure (囗, four-sided wall) containing a weapon (戈, dagger-axe), people (口, mouths), and ground (一). Encoded definition: "the place where people and land are defended by force." This is the original character, in use for two millennia. — Japanese shinjitai 新字体 国 / Simplified 简体 国: the enclosure now contains 玉 (jade / treasure). New definition: "what is precious within walls is the country." Both 1949 PRC simplification and earlier Japan reform converged on the same simplified form, but for slightly different reasons.

Knowing both forms is essential for reading across the CJK scripts: you will see 國 in Hong Kong, Taiwan, classical texts, and traditional Japanese signage; you will see 国 in mainland China, modern Japan, and Korea (Korean uses 國 in 한자 contexts but Korean rarely writes 한자 in modern text).

Mandarin: guó, rising 2nd tone. Names every nation: 中国 (Zhōngguó, China), 美国 (Měiguó, USA — phonetic-meaning hybrid: "beautiful country" but the "Měi" syllable is from "America"), 英国 (Yīngguó, UK — "hero/elite country"), 法国 (Fǎguó, France), 德国 (Déguó, Germany — "virtue country"). 国家 (guójiā, nation), 国旗 (guóqí, national flag), 国王 (guówáng, king).

Japanese: on-reading コク (koku) in compound names — 中国 (Chūgoku, China; or also: a region of western Japan), 韓国 (Kankoku, Korea), 米国 (Beikoku, USA — "rice country", an older calque), 国家 (kokka, state), 国民 (kokumin, citizens). Kun-reading くに (kuni) is the everyday word — 国 (kuni, country), お国 (okuni, your home country / hometown — polite), 隣の国 (tonari no kuni, neighboring country). Many Japanese surnames embed it: 中国 districts, 国吉 (Kuniyoshi), 国民 (kokumin) etc.

Memory aid: walls around a treasure — what each people calls "ours."

In Japan·国 = country (modern simplification of 國)

In China·国 = same simplification, used in PRC