Who makes decisions to manage or regulate conflict in our society? How are those "decision-makers" selected and by
whom?

The correct answer to this open question is the following.

Who makes decisions to manage or regulate conflict in our society?

The federal government, the state government, the United States Congress with its two chambers(the House of Representatives and the Senate), and the judicial branch with all of its courts.

How are those "decision-makers" selected and by whom

United States citizens have the right to select the President of the United States and their representatives at the federal and state levels.  That is why they vote.

The leader of the United States is the President, who also is the chief of the executive branch and its cabinet. He is the most important decision-maker. At the state level, it is the governor. However, the US Congress and the state's congress also play a key roll in creating legislation.  

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