Both Uses of

intervene
in
Utopia, by Thomas More

Every child is nursed by its own mother if death or sickness does not intervene; and in that case the Syphogrants' wives find out a nurse quickly, which is no hard matter, for any one that can do it offers herself cheerfully; for as they are much inclined to that piece of mercy, so the child whom they nurse considers the nurse as its mother.†
*

intervene = get involved or come between

It is certain that all things appear incredible to us in proportion as they differ from known customs; but one who can judge aright will not wonder to find that, since their constitution differs so much from ours, their value of gold and silver should be measured by a very different standard; for since they have no use for money among themselves, but keep it as a provision against events which seldom happen, and between which there are generally long intervening intervals, they value it no farther than it deserves—that is, in proportion to its use.†

Definitions:

(1) (intervene as in: intervened in the war)
the process of getting involved to influence an outcome
The exact meaning of intervention can depend upon its context. For example:
- "intervention program for at-risk youth" -- a process of trying to influence the direction of someone's life
- "medical intervention" -- action taken to improve a medical outcome
- "military intervention" -- interference by a government in affairs of another government (in this case to interfere militarily)
- "had a family intervention" -- an organized meeting of family members to encourage someone (who is often surprised) to recognize and work at solving a problem such as substance abuse
(2) (intervene as in: in the intervening years)
something between two other things -- especially the passage of time between two events
(3) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, intervene can mean:
in various senses, including:
- to verbally interrupt -- as in "Not now!' she intervened."
- to be physically between -- as in: "You can't walk from one hill to the other because an impassable river intervenes."