Why did crises like the cuban missle crisis , the vietnam war , or the berlin wall crisis not develop into war

the answer is d. selective incorporation. (apex)

populist movement, in u.s. history, politically oriented coalition of agrarian reformers in the middle west and south that advocated a wide range of economic and political legislation in the late 19th century. thus in 1892 their leaders organized the populist, or people's, party, and the farmers' alliances melted away.