The semicolon ( ; ) has three main uses in modern English.
1. A semicolon separates two closely related or similarly constructed independent clauses—for example:
Those drinking more than six cups of coffee a day were at 40 percent lower risk for diabetes than nondrinkers; the figure for those who drank less than a cup per day was just 4 percent. [New York Times]
Without the document of 1787, there would have been no United States; with it, the conflict over slavery as the nation expanded became inevitable . . . [You Don’t Say]
2. Semicolons separate list items that contain internal commas—for example:
Ms. Milgram, citing her oversight responsibilities for New Jersey nonprofits, filed suit on Sept. 17, naming Dr. Raveché; Lawrence T. Babbio Jr., the chairman of the institute’s board and a former Verizon president; and the Stevens trustees as defendants. [New York Times]
3. A semicolon may be used to produce a stronger pause than a comma. Such semicolons are often followed by conjunctions, especially but.
Yes, he had legislative victories; but he didn’t show that Congress can make hard choices and act responsibly, because he never asked it to. [New York Times]