"The supreme geopolitical fact of the modern era is that Americans speak English". -- Otto von Bismarck (19th century German chancellor)
First, yes, it is clear that the British and Americans did not always have good relations (See: American War of Independence; War of 1812).
However, towards the end of the 1800s, the British and Americans came together in what is sometimes called the "Great Rapprochement". An essential catalyst to the forming that reconciliation was the British wanting to form alliances with other nations out of self-defense against Germany (at that time, a newly unified state) which the British saw as a rising threat.
The culturally-similar (English-speaking, constitutional, liberal-democratic) United States was a relatively easy/natural ally to make, as the quote above from Otto von Bismarck suggests.
Sources:
On the 'Great Rapprochement'; Bismarck quote
Political Similarities between the US and Britain
The constitutional nature: U.S. Constitution; English Bill of Rights; English common law
The democratic nature: Jacksonian Democracy ushistory.org; [British Reform Act (1832) expands the vote] (https://mcsold1.monet.k12.ca.us/schools/TeacherWebsite/7-12/Fong.M/World%20History/CH%2008%20Growth%20of%20Western%20Democracies%20256-280/Ch%208%20Sec%201%20text%20for%20online.pdf)