I've recently been listening to Dan Carlin's Hardcore History. A topic that comes up early on is the extreme changes that War itself went through between the 19th and 20th centuries.
The technological changes in just a few decades were massive, introducing machine guns, chemical weapons, and artillery that dwarfed any weaponry used in the past.
Many armies were slow to react to the new playing field. There had not been a major war between the Great Powers of Europe since the Napoleonic war. With these extreme advances in technology, once reliable strategies like Cavalry charges and arranging soldiers into Battlefield Drill Formations became obsolete.
Reinforced forts with machine guns and artillery were capable of slaughtering armies attempting traditional advances, and in turn artillery was developed capable of smashing these forts. Many armies suffered extreme losses before adapting to this change in the nature of combat.
I feel that we are in a somewhat analogous point in history. There has not been an all-out war between major world powers since WW2.
From what I'm aware, a vast majority of modern military strategy is focused around the concept of fighting an insurgency/guerilla style opponent. I know that individual nations, as well as organizations like NATO, conduct War Games to simulate large scale conflict scenarios of course. I'm not a military expert, but I feel that most would agree a "World War" scenario in our current world would more than likely result in nuclear war fairly quickly.
I am curious what large scale conflict between two major world powers in today's world would look like, with no nuclear weapons.
What does the attack/defense of a city look like between say, England and Germany? or The U.S. and China?
How would you attempt to secure a region against an opposing army with state-of-the-art modern technology?
EDIT: I think after reading some of the responses a few clarifications are necessary:
1.) I am NOT concerned with geo-political issues. Whether a war is or is not practical does not matter. The nations are at war. The practicality of certain strategies to win that war would be part of what I am interested in.
2.) In this hypothetical, a proxy war is NOT an option. I understand that in practicality a war like this between two major powers would more than likely not happen. This is a hypothetical. In this hypothetical, Country X has committed or is believed to have committed some atrocity on the people of Country Y. No allies are involved. The countries are at war, with the goal being to conquer the enemy's territory and destroy their ability to make war.