intervene, step in, interfere, interpose

get involved, usually so as to hinder or halt an action; "Why did the U.S. not intervene earlier in WW II?"

• poke into, intrude into, meddle with, horn in — poke one's nose into
• meddle, tamper — intrude in other people's affairs or business; interfere unwantedly
• interlope — encroach on the rights of others, as in trading without a proper license

• interact — act together or towards others or with others