To undermine Michael's international success in the 90s is like hiding a mammoth under a blanket.
Dangerous was the biggest selling album by a male artist of the 90s (biggest selling New Jack Swing album as well) while Black or White was Jackson's greatest hit ever - it reached the top 3 (it topped in around 24 territories) in 26 territories whereas Billie Jean which is untruly considered to be his biggest smash reached the top 10 in 21 with considerably less number ones. Dangerous also had 7 top ten singles in the UK which was a record for any album until 2013.
Remember the Time reached the top 10 in 17 territories (Smells Like Teen Spirit which was considered to be a megahit reached the top 10 in 15 territories - do you get the picture now?) whereas Heal the World achieved the same feat in 16 territories, In the Closet in 13 territories and Who Is It in 11 territories.
HIStory had two record breaking singles - Scream which debuted at #5 in the US (highest debut at the time on the Billboard top 100) and was a top ten hit in 14 territories whereas You Are Not Alone broke Scream's record and debuted at #1 in the US and reached the top ten in 19 territories - topping the charts many times as well. Earth Song reached the top 3 in 11 territories. They Don't Care About Us was another smash breaching the top ten in 17 territories. Blood on the Dance Floor also charted within the top ten in 16 countries. HIStory also had 6 top ten UK singles - an achievement even Thriller didn't attain.
Then there was You Rock My World in 2001 which was a top ten hit in 23 territories.
Madonna on the other hand had much less consistent hits - and she had released around 30 singles in the 90s. She had 11 singles which charted within the top tens of at least 10 territories out of the 30 total singles - none of her singles broke through the top tens in more than 19 countries whereas MJ had one.
MJ too had 11 singles which charted within the top tens of at least 10 territories. However, MJ released considerably less singles compared to Madonna - only 20 singles. His singles like They Don't Care About Us and Heal the World and Who Is It did not chart as well in the US - however, the international success was indeed astounding.
Additionally, the tour grosses of MJ's concerts broke records and the HIStory Tour still holds a world record.
Moreover, HIStory was and still is the biggest selling double album of all time with more than 20 million records sold worldwide (40 million units). Blood on the Dance Floor was and still is the biggest selling remix album of all time with 6 million albums sold across the globe.
So my point is that even though Michael's success was declining in the US, his international success and overall standing did not waver much. Madonna might have been outdoing Michael in the US, but Michael was still the king to the rest of the world.