Negative emotions gradually grew into negative sentiments and the companies began to see each other as being incapable of doing business. As a result, they started to treat colleagues from the other company badly. Controls were tightened, trust undermined and disputes arose. Finally, several years later, the acquirer decided to divest. This cautionary tale is from an article on the INSEAD business school website.
Part of the problem was also that people preferred sending e-mails rather than meeting face-to-face. The messages filtered out emotions which remained hidden and therefore were not dealt with. In other words, the true level of dissatisfaction on both sides could not be made clear.