Much as I would like to think that - I don[t agree with you on this!
The UK is not - never was - the "junior partner" in terms of genocidal colonialism. We kind of, sort of, literally helped invent that in its modern sense! Long before the US eclipsed the UK in power, we enabled it to take shape in its current form by colonising North America and wiping out its native population!
Or ... to paraphrase that famous Mitchell & Webb sketch: "not only are we the baddies - we actually sort of wrote the manual!"