Well, it is difficult to call a war fought on 5 continents a regional one.
Since 1939 most of Europe, all Africa, big chunk of Asia, Australia and well, until then of America only Canada, some Caribean and South American.
While, yes, technically, one could call the 2nd Sino-Japanese war in 1937 a regional one (still a bit difficult if literally hundrets of millions of people are involved to call it regional... or rather only if shortly afterwards even billions get involved and it becomes easier to list the countries not at war than those at war).
Objectively, Hitler started a biggest regional war in Europe, but not a World War.
The British dominions and minor allies scattered all over the Planet, who sent their troops to Mediterranean, do not turn a regional European War into a World War, otherwise all wars involving the British Empire automatically = World Wars, which is absurd. (Would a hypothetical British - Irish war = World War, just because Nepal sent several battalions to help British Empire?)
The European battle theater in 1941 (From Narvik to Alexandria / from English Channel to Don) practically did not differ from the usual European battle theater since the Roman Empire and the Middle Ages - the Mediterranean, Britain, Germany, Scythia.
Even the Crimean War of 1863-1856 was much more a World War than War in Europe in 1941 (!)
Then in 1854 the French and British besieged not only Sevastopol, but also Petropavlovsk-Kamchatsky, located in the
Pacific Ocean (!)
If the war in Europe in 1941 was a "World War", then in the history of Europe it is necessary to accept many other "World Wars" before it.
In 1941, all combat operations were limited to the usual European theater + ordinary corsair operations in the world ocean, without transferring the War to land in other parts of the World. (And in parallel there was another biggest regional War in Asia, since 1937, and these two biggest regional wars did not intersect with each other at all, before December 7)
It was Japan that turned two
separate biggest regional wars into one
common global World War, attacking Britain on December 7, 1941.
I do not seek to justify Hitler in starting terrible War in Europe, I just say, if to start from the
facts and
basic logic (and for one minute imagine that Europe is not the center of the Universe), then the real beginning of
real global WW2 is December 7, 1941.
So, Hitler really didn't "start WW2", he started the European part of WW2, two years after the Japanese started the Asian part of WW2.