The US Senate requires a supermajority to pass any bill — 60 votes. But technically, it’s not the actual bill that requires 60 votes. It’s the vote to end debate, which is required to get to the vote.
In the early days of the Senate, it only took a majority to end debate. But in 1805, a change was proposed. Vice President Aaron Burr was being ousted from politics after shooting and killing his rival, Alexander Hamilton, in a duel. In his farewell speech to the Senate, he laid out a handful of things he thought should change — and he specifically critiqued the rule that allowed a majority to end debate.
The Senate got rid of it the following year. This meant debates could go on for as long as a senator (or a group of senators) could stand up and talk. This was the beginning of the Senate filibuster.
To be clear, filibustering wasn’t the only way to obstruct the passage of a bill. Both House and Senate minorities employed other tactics to stop bills they didn’t like. But it’s this tactic — the endless prolonging of debate — that stuck around. And in recent decades, it has caused the Senate to become completely gridlocked, which is why it’s become an issue in the 2020 presidential election.
Some reading that helped me with this piece: