turn of the tide

A dramatic change or reversal of something, especially a given side's advantage in a competition or conflict. The victory marked a turn of the tide in the war, as allied troops began reclaiming more and more territories overtaken by enemy forces. They were hopeful the success of their latest piece of hardware would prove to be a turn of the tide in their position in the market.

A reversal of fortune, as in This last poll marked the turn of the tide, with our candidate gaining a sizable majority. Similarly, to turn the tide means "reverse a situation," as in The arrival of reinforcements turned the tide in the battle. This idiom transfers the ebb and flow of the ocean's tides to human affairs. Although the idea is much older, the precise idiom dates from the first half of the 1800s.

A reversal of fortune. The changing ebb and flow of the ocean’s tides have been transferred to human affairs for many centuries. Shakespeare pointed out the parallel and used it metaphorically in Julius Caesar, in one of his most often-quoted passages: “There is a tide in the affairs of men, Which taken at the flood, leads on to fortune” (4.3). In the nineteenth century the current cliché became common. Edward Bulwer-Lytton used it in The Last of the Barons (1843): “This speech turned the tide.”