Without that, the modern era would probably never have happened. That is because one state would have probably converted Europe into an empire, dominated by a single culture and religion, instead of the great competition of ideas and technologies that happened because there were so many independent states.
The dominant continental powers have been Rome, France, Germany and Russia. Each have, to put it mildy, their own special characteristics.
* Rome conquered and held on to (most of) Britain.
* France was Britain's neighbour. Each was a potential invader of the other right through the middle ages and most of the modern period.
* Up to 1945, Germany was an extraordinarily belligerent power that made enemies of just about everyone.
* Similarly Britain was a rival of soviet Russia only as part of a broader alliance that went far beyond any attempt at realpolitik.
For all the noise and heat regarding the EU, post cold-war Europe is a remarkably friendly place. By historical standards, there is "against" any more.
(I believe this is also why Britain joined the EU in the first place - it's not a threat if Britain has a seat at the table.)
The upshot of this is that Britain was always going to enter WWI once it looked bad for France - if not Belgium, some reason would have been found.