The American policy did much to escalate the conflict.

Answer: Option B

Spread : open out (something) so as to extend its surface area, width, or length.
Develop : grow or cause to grow and become more mature, advanced, or elaborate.
Reduce : make smaller or less in amount, degree, or size.
End : a final part of something, especially a period of time, an activity, or a story.
Escalate : make or become more intense or serious.
Synonym of Escalate is Develop