War was a contest of industrial strength and overall national power.
Industrial strength went without saying. Simply put, it was a matter of seeing whose weapons ran dry first.
Of course, that was only when the technological gap was not too great. If there was an enormous disparity in technology, that premise no longer held.
For instance, once the Osborn Group had successfully taken to space and established off-world Colonies, Earth could no longer go to war with the Osborn Group. They were no longer on the same level.
Overall, the war between Thanos and the Osborn Group was still limited to a contest of fleets, continuing until one side destroyed the other's final production facility and killed its last soldier.
But Thanos's war technology was not advanced.
As for ground forces, the Chitauri's terrible equipment had been clearly demonstrated during the Battle of New York.
Old-fashioned firearms were remarkably effective against them. Such a situation would never arise within the Osborn Group.
Even the lowest-ranking Rifleman could not be pierced by rifles from the old era. In contrast, a Piercer Rifle could easily punch through the frontal armor of the previous generation's main battle tanks.
At sea, the only thing Thanos could truly put forward was a Flagship. His other spacecraft were fragile paper airplanes.
Besides, the Osborn Group's weapons generally had extremely long range. Their Flagship was merely a slightly tougher target.
Thanos's sole advantage was numbers, but now even that advantage was about to disappear. He lagged behind across the board in both war technology and industrial capability.
The Gigantic Shipyard would completely concentrate the industrial capacity of the entire Star Sea Community and bring it fully to bear.
As for overall national power... Thanos's Legion was, at best, a pirate gang that happened to be large