This is strange to me, since 1) Japan had trounced Russia on that front previously, 2) Soviet fortifications in the Far East don't seem to have been too impressive, 3) it was a long-held ambition of Japanese nationalists (like Tojo himself) to take the Siberian coast - as well as holding some decent real strategic value, and 4) the wartime Japanese Empire isn't exactly renowned for its realistic calculation of enemy capabilities.
Given all that - unless I'm incorrect on any point - why were Japan so ready to seek neutrality with the Soviets? Were the Khalkhin Gol incidents really such a defining conflict, and why?
More can be written, but you might like to start with "Why didn't Imperial Japan Declare War on the USSR in support of Nazi Germany?" by /u/Patsbrav88 and /u/pizzapicante27 . As well, /u/kieslowskifan had a number of replies at and under "Why did Hitler and Mussolini declare war on the US to support Japan when Tojo/Emperor Hirohito didnt declare war on the USSR in support of Germany and Italy?" . This main reply covered Japan's war decisions; two replies below cover Japan's use of southern war materials, and the consequences of Khalkin Gol.
But this is not to discourage discussion. More questions, data, and debate are welcome.