An incident at the gulf of tonkin, off the eastern coast of became the justification for increasing the level of u. s. involvement in the war in vietnam during the johnson administration. north vietnam south vietnam cambodia china

b.   jim crow laws were enacted in northern states.

climate change is the big reason to the decline of the indus valley which also caused floods. so i dont know what answer would best fit the description thats just what i found online! have an awesome