Interventionism is the belief that a government or a big organization should step in — spend money, make rules, or even use force — to change how the economy works, or to change what happens in another country. An interventionist government might try to save jobs, hold prices down, or get involved in a war abroad. People who want markets to run with little control often use the word as a criticism: they think the government should stay out. People who want the state to help the poor, steady the economy, or keep peace may accept the word more calmly. It is a politics and economics word, quite formal. The -ism is the idea, the habit of stepping in, not one single act.