The British have dealt with tanks since about 1911. In all countries, many designs of armored vehicles appeared, I think that the appearance of tanks was only a matter of time. Roughly the same goes for the SMG, designs like SMGs have been around since the 1890s, sooner or later someone would have done it.
In general, I think that most of the novelties of the First World War period would have appeared anyway. And I think you shouldn't underestimate the arms race. By the beginning of World War II, thanks to the arms race, and not some big war, countries came up with the ideas of MBT, AT rocket launchers, helicopters, etc. Why can't the development of armored vehicles give an impetus to the development of tanks? Especially by the 30s.
In terms of the economy, Russia occupied the first place in terms of growth rates, Germany occupied the second place, France and Britain began to lag behind, Austria-Hungary and Turkey were gradually fading away.
I think there will be many different wars on the outskirts. Britain and Russia could agree to an agreement on the division of Turkish possessions, the Russians would like to get the Bosphorus, the Dardanelles, the southern and eastern coasts of the Black Sea, the British would like to get the Middle East, possibly the islands. Persia would have been a contested territory of influence between Russia and Britain, perhaps a mutually beneficial agreement would have been reached.
Austria-Hungary is likely to fall apart. Immediately, part of the territory will be taken by Germany, or, by annexing the whole of Austria-Hungary, the Russians will most likely demand the western territories.
France and Britain will continue to expand in Asia, most likely, there will be a confrontation between them, Russia and Japan in this region.
If fascism comes to power in Italy later, then most likely there will be an attempt to expand into the Balkans and Africa, a clash with Britain is inevitable, France and Russia, depending on relations with Britain, can support either the British or the Italians.
At the same time, Germany will remain a strategic enemy of France and Britain.
The role of the United States is difficult to imagine, because on the one hand, it is unprofitable for them to have competitors on the world stage, be it Germany or Russia. On the other hand, she can easily make friends with both Russia and Germany, and at the same time fight against Britain.
At some point, Russia will try to return the islands selected by Japan in 1904-1905. This means a conflict with Britain.
Will there be a revolution in China? Unknown. Unlikely.
There may be other conflicts as well.
I do not know the reasons for the revolution in Germany and Russia if peace is preserved. The German revolution began because of the lost war and because of the famine, the Russian revolution actually started only after the coup of February 1917, when a group of conspirators took advantage of the turbulent situation in Petrograd (despite the fact that there were several times less protesters than in 1905). At the same time, both Germany and Russia had a fairly developed working legislation.
For quite a long time I rummaged in the subject of Russian armaments at the beginning of the 20th century. Here's what they considered promising:
Artillery:
1. The re-armament of field artillery with 107-mm cannons and howitzers, using fast all-wheel drive tractors (then the 107-mm cannon and 152-mm field howitzer had the same weight)
2. Creation of powerful siege weapons, at least 406-mm howitzers
3. Development of anti-aircraft artillery, up to the creation of 152-mm guns
4. The introduction of long-range shells, in general, an increase in the range of artillery
5. Perhaps - replacing the M1902 cannon with a more advanced
Small arms:
1. The introduction of long-range rifle cartridges
2. Replacing bolt-action rifles with semi-auto
3. Replacing revolvers with semi-automatic pistols
Fleet:
1. "Squadron cruisers" with 180-mm cannons in 4-gun turrets
2. Battleships with 406-mm and 457-mm guns
3. Increasing the second caliber of battleships to 152-mm or 180-mm
4. Using remote control of all implements
5. Maximum automation of loading
6. A spotter plane on a catapult for battleships
7. Guided torpedoes
8. Submarines with increased power reserve
Aviation
1. Continuation of work on large aircraft
2. Construction of experimental jet engines, turboprop and others
3. Use of wireless radios in aviation
There were many other proposals and different perspectives. In 1915, Russian sailors, who almost did not encounter enemy aircraft, that is, in fact, outside the war, decided that they needed a 25-mm autocannon, a large-caliber machine gun, a 76.2-mm cannon with 700-800 m / s. Sikorsky and Slesarev did not have enough powerful engines to put them on their airplanes, in fact, the creation of engines for 600 hp. and more was just a matter of time.
Other countries should have about the same prospects, but I have not researched this.
SMGs may appear as police weapons. Assault rifles were mainly invented before the First World War, at least the United States, Austria-Hungary and Russia had developments in the direction of creating automatic (semi-auto or full-auto) weapons for intermediate cartridges.
I think that the further the world will live without the First World War, the more dangerous it will become. The fact is that at the beginning of the 20th century, at about the same time, work on rocketry was going on, as well as research on radioactive materials. Virtually all key countries could have acquired nuclear weapons in the 1940s. But, there was no "lesson" in the form of the death of tens of millions of people. What will happen in this world? Nuclear WW1? Which will last approximately 1 day. Someone can resist a preemptive strike? Given the very small likelihood of the existence of at least some kind of warning system about the launch of missiles by the enemy, because the electronics will still not be able to do this. Wilhelm II spoke of "racial war". Imagine the Caribbean crisis with such a fanatic instead of Khrushchev. There will be a boom.
