To come, appear, or lie between two things: You can't see the lake from there because the house intervenes.
To come or occur between two periods or points of time: A year intervened between the two dynasties.
To occur as an extraneous or unplanned circumstance: He would have his degree by now if his laziness hadn't intervened.
To involve oneself in a situation so as to alter or hinder an action or development: "Every gardener faces choices about how and how much to intervene in nature's processes” ( Dora Galitzki).
To interfere, usually through force or threat of force, in the affairs of another nation.
Law To enter into a suit as a third party for one's own interests.