From the Latin "intervenire," meaning “to come between,” the verb intervene means just that: to get involved, to jump in the middle of something, to interfere.
The verb intervene was first recorded around 1600. Since then there haven't been many interventions in its meaning or usage. You should probably intervene in a heated verbal fight between two of your friends before it escalates and gets physical. Especially if they're debating the United States’ habit of intervening in international conflicts.