We DID stop Hitler! OK, so we should have perhaps done something earlier but we warned him if he invaded Poland we would declare war and we did.
Slavery? We could not have contributed to that without the help of some African tribesmen wh were willing to sell their members to slave traders. We abolished slavery long before America.
Hong Kong? We created a wealthy territory. OK, the politics was all wrong but we've done what we said we would do - leased it for 100 years then handed it back.
Do not forget, many brave Brits volunteered to serve in the Spanish Civil War too, wading in when many nations stood back and let facisim (helped by the Catholic Church) get a grip on the Spanish nation.
On reflection, we have a lot to be proud of.
