I was thinking of starting a thread on examples of vote splitting under FPTP, but we may already have had one here. So I will go further, listing examples of candidates quitting to avoid vote splitting.
A suspected example of that was over the two days before Super Tuesday, March 3, 2020. On March 1, Pete Buttigieg dropped out, and on March 2, Amy Klobuchar dropped out. On the latter date, both candidates endorsed Joe Biden. Pete Buttigieg And Amy Klobuchar Endorse Joe Biden : NPR
Some people consider it very suspicious that they dropped out when they did, just in time for Super Tuesday. It is presumably to avoid splitting the moderate, centrist vote among them and JB, thus letting Bernie Sanders win non-majority pluralities.
New York City has two recent examples in its Democratic Congressional primaries. NY-14 in the Bronx and Queens
Incumbent Alexandria Ocasio-Cortez faced six challengers in the Democratic party, though three of them dropped out before the primary election. Bronx councilman drops bid against AOC to run for borough prez
mentions the decision of challenger Fernando Cabrera to drop out when challenger Michelle Caruso-Cabrera entered the race. FC then endorsed MCC so as not to split the anti-AOC vote.
Another Democratic challenger claimed that she received a "veiled threat" from a campaigner for a rival candidate
In the general election, AOC will be opposed by the only Republican out of eight to make it to the primary ballot, another Republican running as a write-in, another Republican running as an Independent, and MCC also, a former Republican who is supported by another party. NY-16 in the Bronx and Westchester County
Long-time incumbent Eliot Engel faced four challengers, notably Jamaal Bowman and Andom Ghebreghiorgis. Jamaal Bowman Gets Backing From Engel Challenger
describes AG's decision to drop out and support JB. He did it to avoid splitting the vote for his side.
Any more such examples?