The correct answer to this open question is the following.
Although there are no options attached we can say the following.
You did not specify a time in history, a place, that could help us to answer the question, because humans have always waged war since the ancestral civilizations of Sumeria, ancient Egypt, and the Indus Valley, up until today.
We are going to assume that you are referring to the World Wars period, to have a more direct answer.
So we can comment on the following.
Some similarities and differences in the methods governments used to conduct war were the following.
The advent of new discoveries improved the technology used in the fabrication of weapons, machines, tanks, airplanes, and warships.
If we are focusing the answer in the World Wars period, w have to say that World War I was considered to be the first total war, which means that the governments were capable to use any strategy, allowed or not, ethical or not, to totally defeat the enemy and win the war.
So that could be one similarity. Nations started to use this total war approach to win wars and completely defeat the enemy so it could not represent a further threat to the victorious nation.
Another similarity is that countries started to sue propaganda, campaigns and mass media such as radio and the newspapers to have the support of their citizens to go to war and make internal sacrifices for the benefit of the war effort.
The difference could be that not all the nations had the power, economy, and infrastructure to wage war the same way and were at disadvantage against other powerful nations. That is why, in some notorious moments, nations have formed alliances to wage war as was the case of the Triple Entente or the Axis Powers, to joining forces aspiring to have better results.
