How can we be asking whether "国家主義" means "nationalism", when the meaning of nationalism itself is very fluid? You have provided one context sentence to fix your particular meaning of nationalism: "wanting to re-build the Imperial Japanese Empire". But that can surely be described specifically as as "imperialism" and "militarism". Is "nationalism" equivalent to "imperialism" and "militarism"? It is true that in times of large scale political change, we are likely to see "nationalism" and "imperialism" and "militarism" appearing more often (along with several other ism's as well). So there is correlation, but correlation does not imply causation.
We are now living in the age of Globalism, a term that includes a range of phenomena extending from higher ideals such as global cooperation on climate change, global peace, elimination of disease and hunger, all the way down to the race to the bottom in workers wages and working conditions, sweeping of industrial pollution under foreign carpets, and under-utilization of human potential in advanced nations.
We now see Nationalism rising in response to the darker side of Globalism. Maybe, instead of reacting violently against either, we need to find a way to let the better parts of Nationalism and Globalism coexist, while leaving the worst of both behind.
We shouldn't be in any rush to define "国家主義" as something a priori bad. It's one the many natural ～主義 in our social gut which when holistically well balanced keeps us healthy, but when not makes us sick.
Edit: According to Wikipedia, "nationalism can be positive or negative".
Nationalism is a complex, multidimensional concept involving a shared communal identification with one's nation. It is a political ideology oriented towards gaining and maintaining self-governance, or full sovereignty, over a territory of historical significance to the group (such as its homeland). Nationalism therefore holds that a nation should govern itself, free from unwanted outside interference, and is linked to the concept of self-determination. Nationalism is further oriented towards developing and maintaining a national identity based on shared characteristics such as culture, language, race, religion, political goals and/or a belief in a common ancestry. Nationalism therefore seeks to preserve the nation's culture. It often also involves a sense of pride in the nation's achievements, and is closely linked to the concept of patriotism. In these terms, nationalism can be positive or negative.