-Try finding 8 million Ukrainian died during WWII on the internet. (6.7 million is the highest citation of Ukrainian deaths for WWII I could find offhand (Wiki rounds that up).) It is not of casualties of war time resistance to the Nazis but of total casualties, meaning we don't know who died doing what.
Bono parroted a lie from the President of Ukraine while the nation is in a giant untertaking to lie about its history, overseen initially by one man. He claims that 23% of the USSR's army resisting the Nazis was Ukrainian, so take that with the requisite grain of salt. Ukraine was just as civilly divided then as they are now, a true tragedy of WWII. They fought on both sides, with the fascist, murderous faction even switching sides when they realized they weren't actually allies with the Nazis, that the promise of an independent Ukraine was illusory, but that didn't apprehend the slaughter. As recorded, they just went independent with it. (The one million Jews who survived the Ukrainian Holocaust survived by fleeing to the USSR.) When the Nazis invaded Ukraine, the OUN (Ukrainian independence revolutionary faction) didn't just march with the Nazis into town, they started the pogroms ahead of the Nazi invasion in full awareness of what was coming. The embrace of Nazism by Ukraine's independence revolutionaries represented their perceived liberation along ethnic purification lines, officiating prior unruly pogrom outbreaks Ukraine had already carried out in the past. Ukrainians had already killed 100,000 Jews from 1918-1921. (OUN was created in 1929.) The Nazi invasion allowed them to go on to kill 100,000 Polish civilians (the Volhynia/Volyn/Wolyn Massacre), as well as 1.5 million Jews, -Encyclopedia Britannica.
The targeting of journalists and historians by foreign embassies and the like shows this history is high stakes, highly contested territory. It's not place to be bandying about unqualified figures, but with that in mind, as per 6.7 million Ukrainian fatalities in WWII, you can deduct 1.5 million Jews the Ukrainians had a heavy hand in exterminating themselves in some of the worst internecine savagery ever carried out in Holocaust. Ukraine's hallmark in WWII history is the ignominious position of presaging the Holocaust in terms of the first Jewish pogrom wave that proceeded to "normalize" such atrocity during the throes of the Russian Civil War/post WWI, and then they proceeded to get it off ground with mass killing by munitions before the corporations officially industrialized it, putting it to maximal slave labour use/gassing them conveniently out of sight. In Ukraine, it wasn't out of sight. It was carried out town by town by the locals aiding the OUN/auxilliary police who later joined the UPA, and they would use drowning, stoning, sticks, axes and farm tools in lieu of bullets (the adds to that list are Himka's).
In other words history is complicated, and Bono's figure isn't dared by the worst of the present historical revisionists because it would be met with laughter as opposed to credulity, revisionists that are only in key positions because they service the current US neocon/neoliberal agenda. A cursory review of bandied about figures is enough to know that Bono's humanitarian appeal sound byte is patent BS: that's as easy as citing the total death toll for the USSR's army (8.66 million), given Russia suffered the highest mortality rates both army and civilian, and the vast bulk of Ukrainians who would have resisted the Nazis would have served in USSR's army. (USSR's army deaths were 9.75 million according to a WWII Scholastic altas by Sean Callery, which lists 31 countries' combined millitary and civilian deaths for WWII, with Ukraine again absent from the tally.) Even by most the most historical revisionist figure that nearly a quarter of those fighting in USSR's army were ethnically Ukrainian, a number of 8 million dying resisting the Nazis is not remotely approachable. The 1.5 million Jewish dead within the present day borders of Ukraine comes from qualified historians. The history itself is a contentious minefield, nowhere more so, it appears, than the University of Alberta.