What does the author mean when he says that there was a "rift" between publishers and Amazon?

Question

From "Amazon.com." Encyclopedia Britannica. Encyclopedia Britannica Online School Edition. Encyclopedia Britannica, Inc., 2013. Web. 10 Jan. 2013.

'The Kindle Shakes Up Publishing'

By 2010 the rift between book publishers and Amazon.com over the price of e-books had grown. The publishing company Macmillan Books threatened to pull its e-books from Amazon.com, which retaliated by removing all Macmillan books, both printed and electronic, from the site. However, within weeks, Amazon.com capitulated and allowed Macmillan and other publishers to set prices of e-books.

A.They cooperated gladly.

B.They disagreed strongly.

C.They appreciated each other.

D.They misunderstood each other.

Answer 1

B.

The reason is because of words such as "threatened" and "retaliated".