That's according to UK Foreign Secretary David Cameron, Ukrinform reports, citing The Sun.
He stressed that Britain must understand how the world has changed.
"The forces shaping it – a warmonger in the Kremlin, a more aggressive China, Islamist extremism poisoning young minds – these things aren't going to disappear overnight. There's no point hoping for some magical return to the world as it once was," Cameron said.
He added that hope is not a policy.
"If Putin isn't stopped in Ukraine he will be back for more. And we know from our history that appeasing dictators ultimately wrecks British interests and costs British lives," Cameron said.