Why did the conflicts and crises of the first half of the 20th century become global in nature?

20th-century international relations, history of the relations between states from about 1900 to 2000. The first half of the century was dominated by the rivalries

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explanation:

the monroe doctrine is the best known u.s. policy toward the western hemisphere. buried in a routine annual message delivered to congress by president james monroe in december 1823, the doctrine warns european nations that the united states would not tolerate further colonization or puppet monarchs.