@SunAcrossWater to expand on what's already been said. The English are an insulary people with a singular culture since not long after 1066 AD - historically speaking. There were many English people very unsettled by the large number on non-white immigrants first from India and Pakistan once England lost those as colonial possesions, and later because of EU open border laws. Those who view the west as adversaries saw this and encouraged it through echo chambers and disinformation.
@SunAcrossWater Every chance they got they drove wedges between the native English the non-native. They pushed a narrative that the EU was to blame. That England would be better off without the EU. Eventually English politicians started to "cater" to the "pro-English" crowd. When those driving the wedges saw a politician doing so, they encouraged them to pursue the disruptive discourse by donating to their political campaigns, etc.
@SunAcrossWater They worked on funding anti EU groups, and pointed them to the politicians being groomed for the role. And they just kept at it until they got what they wanted - England out of the EU. The did the same in other countries: the U.S., France, Italy and others. The whole point was to weaken alliances that had been (mostly) rock solid since WW2. And it worked, though the west is slowly starting to figure out how badly they've been pwned.