According to this paper in the Harvard Journal of Law & Public Policy:
The possibility that a minority of Senators could hold unlimited debate on a topic against the majority’s will was unknown to the first Senate. The original Senate Rules...allowed a Senator to make a motion "for the previous question."...This motion permitted a simple majority of Senators... to halt debate on a pending issue....
This motion was a well entrenched tradition among legislatures of the time: It had been recognized by the British parliament since 1604, by the Continental Congress, and by the House of Representatives,...which still observes it to this day.
Today, the previous question motion is generally understood as a method for cloture;... that is how it functions in the House ofRepresentatives... and the British Parliament... where, if passed, it stops debate and forces "an immediate, final vote" on the pending proposal....
Only by accident (or oversight) did the possibility of unlimited debate get established (thanks to Vice-President Aaron Burr in 1806) according to former Senator Clifford Case:
"The fact is that so-called unlimited debate in the Senate is a myth.
History shows clearly that up to the time of the Civil War a
majority of the Senate, under its rules and precedents, and under
the dignity of its customs, did have the authority to, and for the
most part effectively did, limit debate and prevent filibusters… .
There may be exceptions, but the truly representative picture of the
Senate before the Civil War, as shown by our historical records, is
that the body observed dignity and restraint in debate, and did not
consider talking to consume time a parliamentary instrument
appropriate for the Senate… . [T]he filibuster as a device, not
merely to delay, but to prevent, action is a modern institution
which has no support or sanction in early Senate history and
And, in 1917, the practice became intolerable to Woodrow Wilson--in the face of threats by Germany to open unrestricted submarine warfare on American commercial shipping, alongside an offer to Mexico to join with them, in exchange for an opportunity to recover lands formerly belonging to that country, but now States--eleven isolationist senators (led by Robert LaFollette) prevented a vote on a Bill to allow merchant shipping to be armed for protection.
Said Democrat Wilson:
The Senate of the United States is the only legislative body in the world which cannot act when its majority is ready for action. A little group of willful men, representing no opinion but their own, have rendered the great government of the United States helpless and contemptible.
And that led to a change in Senate rules (known as 'cloture') that allowed a two-thirds majority of the Senate to cut-off debate. Over many years of filibusters of Civil Rights legislation attempts were made to loosen that requirement, and finally, in 1975 it was reduced to a 3/5 majority.