The filibuster evolved accidentally. It's not mentioned in the Constitution, nor is it part of our system of checks and balances. No Senate rules specifically mention filibusters.
When the House of Representatives and the Senate were established in 1789, each had similar rules for cutting off debate on a bill or any other matter. Only a majority vote was needed to pass a "previous question motion" [source: New York Times]. Once that motion passed, debate on the bill ended, and senators then voted whether to enact the bill into law.
In 1806, senators simplified their rules, eliminating the little-used "previous question motion" rule, which limited debate [source: Connolly]. They didn't realize that they had made it possible for one or more senators to carry on an endless debate that could keep bills the majority wanted to pass from coming to a vote. The House, on the other hand, retained the ability to cut off debate by a simple majority vote. Filibusters are not possible in that body.
During the 19th century, the filibuster was an uncommon tactic in the Senate. The first filibusters were not held until the 1830s [source: Connolly]. Fewer than two dozen filibusters took place before 1900. The reason was that the Senate had a tradition of reasoned debate and most senators frowned on any abuse of rules.
In 1917, a group of senators conducted a filibuster to block a bill that would arm U.S. merchant ships. Frustrated by the 23-day delay as the Great War raged in Europe, President Woodrow Wilson enlisted public opinion against "a little group of willful men" [source: Carlson]. He pushed the Senate to pass what was known as the cloture rule. That meant that two-thirds of senators could vote to cut off debate.
During the 20th century, Southern senators often used filibusters to block civil rights legislation. From 1922 to 1949, they were able to block five separate anti-lynching laws. In 1957, South Carolina Senator Strom Thurmond spoke in the Senate for 24 hours, 18 minutes in an unsuccessful attempt to prevent a vote on a civil rights bill. His record for a one-man filibuster has never been surpassed [source: Carlson].
In 1975, senators changed the cloture rule to require only a three-fifths vote, 60 rather than 67 senators, to cut off debate. But new procedures also allowed Senators who could muster at least 41 colleagues to block a particular piece of legislation while the Senate proceeded with other business. They didn't need to conduct an actual filibuster, only threaten one. Intended to make the Senate more efficient, this change actually increased the frequency of filibusters [source: Schlesinger].
In the next section you'll read about how a filibuster is actually conducted.