It sort of depends on how you define "terrorism" and "achievements".
France does not rule Algeria or Vietnam today, in part because of violent acts that were called terrorism at the time. The same is true of Great Britain and Palestine/Israel. You could even say that the British settler and government counterrevolutionary response in Kenya was particularly brutal terrorism which succeeded in putting down the revolt but failed long term in keeping Kenya under direct British control.

So sometimes violence/terrorism works; sometimes it doesn't.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.