I'd recommend checking out Japan 1941: Countdown to Infamy by Eri Hotta if you're interested in the topic. It's an excellent look at Japanese politics in the leadup to the war with the US.

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Effectively what Hotta explains is that the Imperial Japanese government was nominally a democracy, but the structure of its government was somewhat hamstrung by a requirement to have the Army and Navy appoint a member each to roles within the cabinet. That meant that, by having their member resign and refusing to appoint a replacement, they could get the cabinet dissolved and effectively strongarm the government into going their way. What made this all the more dangerous was the general attitude among the Japanese populace at the time. As was the case in much of the world, Japanese society was very jingoistic and nationalistic, and Japanese media was very good at getting the populace riled up in favor of things that were often bad decisions on the world stage. A good example of that was the invasion of Manchuria - local forces initiated the invasion on their own initiative and without notifying the government, and despite the government itself being against the move, the media at home managed to get the people to vocally support the invasion until the cabinet accepted it.

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The impact of the war with Russia depends on if you're talking about 1905 or 1939. The 1905 war played into a long series of events that managed to convince Japan that they were both destined to succeed despite all the odds and being held down by greedy Western powers. Like the First Sino-Japanese War, the Russo-Japanese War saw Japan going to war with a massive nation that all observers thought would easily defeat them. Both times, Japan won decisive victories, only for Western powers to step in as negotiations began to force Japan to accept far less than it felt it deserved for winning the wars. Later events would build on the victim complex started by these wars, including Japan's treatment at the victor's table in WW1 and the Washington Naval Treaty.

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The 1939 conflict with Russia, on the other hand, had a vastly different impact. The IJA's grand strategy was generally looking northward up until the Battle of Khalkhin Gol, where the Kwantung Army was so heavily thrashed that the Soviets were poised to sweep through Manchuria nearly unopposed. This caused the Kwantung Army to be seriously reigned in by the government, a non-aggression pact with the Soviets to be signed, and a massive reevaluation of Japanese strategy. Japan from that point on was terrified of the Soviets, keeping peace with them up until the Soviets entered the war in 1945 and shifting their foreign policy south to the Indies. This had the critical impact of shifting Japan's ambitions to where they would clash with the US.