Do individuals have a greater impact than lager groups in society in starting war?

Usually, it depends on the situation in question. Sometimes, a single person can provoke war from a country by committing an atrocity to spur a reaction from the target country, hopefully, in their minds, achieving their goal, and the country declaring war. In some instances, a group can fan out to provide an even more crushing blow to a country, or start a hostile movement against another country, ideally provoking others to join them in arms.