The phrase "takes up arms" historically refers to individuals engaging in armed conflict or warfare. Synonyms for this phrase include "wages war," "fights," "battles," and "becomes a combatant." Additionally, "arms" could be replaced with other weapons or tools used for combat, such as "takes up arms with swords," "takes up arms with guns," or "takes up tools for battle." However, it is important to remember that armed conflict should always be a last resort and that peaceful conflict resolution should be prioritized whenever possible.