Does the involvement in imperialism and slavery by other European nations justify our history?
Let's look at King Leopold of Belgium.
King Leopold was the absolute ruler of the Congo free state from 1885 to 1908 and during his rule, an estimated 10m to 15m Africans died, which led to the first use of the term "crime against humanity".
He used forced labour, murder, torture and atrocities, to extract a fortune from the country, from their rubber and ivory resources.
The hands of men, women, and children were amputated when the quota of rubber was not met.
Are we balancing all that against some undefined benefit Congo has received from being colonised?
I'd say other European countries should be having a good look at their own history too and ensure they aren't glorifying slave traders, murderers, torturers, etc...
You need to read up on the history of empire, especially the Mau Mau uprising in Kenya to see the disgraceful role our country played in creating the largest concentration camp on earth.