The poem was one Emperor Meiji composed on the eve of the Russo-Japanese War. One of the translations in The Sources of Japanese Tradition is this:

On all four seas

I thought all men were brothers

Yet in this world

Why do winds and waves

Now rise and stir?

Hirohito read the tanka of his grandfather on 6 September 1941conference and he asked his two military chiefs of staff what they thought of the poem. The general historical interpretation of this bit of imperial theater is that Hirohito was exerting soft pressure on his counselors to give diplomacy a chance to adjust Japan's relationship with the US.

However, historians of modern Japan like Herbert Bix, Akira Iriye, or Noriko Kawamura have noted it is quite misleading to speak of Hirohito being "forced" into war. For one thing, part of Hirohito's reinvention in the postwar period was to describe the Emperor as a sort of peaceful monarch who was more interested in marine biology than wartime expansion. Thus it became important for both Hirohito and his various defenders to emphasize actions like the 6 September poem recital over less elevated activities like finally sanctioning the war or appointing Tojo as PM. Hirohito may have expressed a desire for a diplomatic solution, but he did not modify Japan's basic negotiation stance which involved very little sacrifices on the part of Japan and was a dead letter in Washington. By the same token, "forced" also implies a degree of compulsion that the military leaders lacked over the imperial house. The services' respective ministers could resign and throw the civilian government into chaos, but they could not directly move against the Emperor. Hirohito failed to build consensus around his positions and while he was able to give glimpses into his apprehensions about war with the US, he was never able to translate this into a coherent policy. The tanka recital may have signaled the imperial house's desire for peace, but it also sanctified a timetable which war preparations would begin in mid-October if diplomacy bore no fruit. The imperial system of Japan placed the Emperor in an ambiguous apex of the Japan's government where he had to build consensus and Japan's problem in late 1941 was the only real, albeit somewhat tenuous, consensus within the central government and the military was the need for war. Finally, it also bears stressing that whatever Hirohito's doubts about the war, he also took Meiji as his model in imperial presentation. His grandfather was the only successful imperial monarch and it makes a degree of sense that Hirohito would look to Meiji when presenting himself to his ministers and his Japanese subjects. The Russo-Japanese War had been the zenith of Japan's imperial power in 1941- it had taken on and beaten a major world power, Russia- and it made a good deal of political sense for Hirohito to invoke Meiji prior to undertaking another war against two major powers.

This does not mean that historians are united on Hirohito's role in the decision for war. There is a lot of variation within the historiography on this topic. Bix and Japanese leftist historians are quite critical of the Emperor and hold that he could have applied the brakes to war more forcefully, but did not. Kawamura is more measured in her criticism noting that Hirohito inherited a clumsy imperial power-sharing arrangement from his grandfather that constrained him in 1941. There is obvious room for argument in this matter, but it is a somewhat dubious thesis to contend that Hirohito was a passive object being forced into war.