Not race, but police culture.
Each country chooses (usually unconsciously) many of their social outcomes. Looking at other countries can illuminate what choices have been made.
The US has chosen to allow its police officers to shoot to kill as a matter of course. This has been allowed because of general sentiment and hard positions on gun control, gun usage and views on individual responsibility and rights.
The result is that in the USA in 2011 over 150 people were killed by police fire. No other advanced western country has anything like that problem.
The UK has chosen not to arm its police generally. Crime levels are not incredibly different between the two countries. Although the UK is only a fifth the size of the USA in population, care to guess how many people were killed by police gunfire in the same period?
Two!
Countries choose their social outcomes.