Japan in 1930 wasnt nationalistic, it was ultra-nationalistic with imperial-expansive-xenophobic elements. Japanese even assasinated their own politicans who did not prefer war and wanted to avoid it. 1930 Japan is pretty much without an equivalent, even Hitler and Mussolini were more carefull of going to war.
Essentially this, but I want to emphasize how bad the government by assassination era really was. Japanese politics in the mid-1930s was such that 11 naval officers could march into the Prime Minister's house, murder him in cold blood, and get off with a slap on the wrist (the May 15 incident). A coup attempt in 1931, the Imperial Colors Incident, sought the assassination of much of the government, including the Prime Minister, Grand Chamberlain, and Foreign Minister, a blanket ban on political parties, and the "restoration" (based on a romanticized view of the Meiji Restoration) of the Showa Emperor against the perceived corruption of the Western democratic government; it ended with a sentence of less than a month's time under house arrest for only two of the ringleaders, and in fact, one of the said ringleaders, Kingoro Hashimoto, would go on to play a role both in politics and the war with China. The secret tribunals and executions that marked the effective destruction of the Imperial Way faction after the failure of the February 26 Incident (which you'll find to be a general naming trend; all of these putch attempts, assassinations, and the like tend to just be marked down in history as little "incidents") was not a triumph of civilian authority over the military, but a power-purge by their political rivals in the military (chief among them Hideki Tojo, who would eventually become Prime Minister), who proceeded to co-opt the faction in their own way.
Essentially, and forgive the edit, government by assassination ended not because militarism had ended in Japan, but because it had won: after the February 26 incident, in spite of the failure of the Imperial Way, the civilian government now served solely at the pleasure of the Army and Navy. The Okada government that formed in the wake of the collapse of the immediately-preceding cabinet in the wake of this incident was compelled to nominate officers based on the preferences of the serving Minister of War, and the military could compel the fall of the government simply by withdrawing the Minister of War and/or the Minister of the Navy while refusing to nominate a replacement, forcing a new cabinet to be formed. Political pressures subsequent to this in the lead-up to World War 2 therefore no longer are a matter of military versus civilian or right-wing versus left-wing, or even between factions within the Army, but rather simply between the Army and Navy: rather than peace or war, it's which nations the war will be waged against.