The sociologist, daniel chirot, argues that the recent worldwide increase in ethnic hostilities is a consequence of "retribalization." by this he means

Daniel Chirot is a Sociologist and Professor of International Studies at the University of Washington, Seattle.

He argued that the recent worldwide increase in ethnic hostilities is a consequence of retribalization.

His context of retribalization means the tendency for groups to seek meaning and belongin in an ethnic group. There are macro and micro explanations for terrorism.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."