Heck, I might as well postulate my own as well as the polish scenario pic.
The polish one is easier. Hitler in that reality tooled the NSDAP's ideology to be more anti-communist and anti-french than anti-slavic (His anti-semitism here is about the same). While still going with the idea of lebensraum (a westward one like the Franks once did), he decides to simply leave off the Danzig Corridor and Poznan off the realm of Germany. He does this seeing as the latter is a decent deal more Pole than German, while in this reality, far more Germans from the corridor moved to either East Prussia or Brandenburg during the 20's.
As a result, Hitler is fairly ambivalent towards polish subjection and would prefer a buffer against the Soviets. Timeline marches about the same to 1938, where he absorbs Austria and the Sudetenland diplomatically. This gives Stalin the idea of annexing the Baltic States (With a Lithuanian exception thanks to German posturing against such a thing). This antagonizes Poland against the soviets, and as a result they go to the German camp.
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My pic theory:
Chiang manages to begin wrangling the army under his control by first redistributing the modern weapons from German and Soviet camps to better equip his current army rather than commissioning more units. He also restarts the Commissars again after his purge of the communist faction in them(long march), to drive morale.
He lets up on the communists somewhat more after evicting them to the mountains of Shanxi province. He only does it only because the Japanese were retooling the Kwangtung army, and he doesn't want to deal with the warlord states and Japan at the same time. He managed to seize control of Guangdong province and the southern factories and trade bolster his country's control.
Japan as a result tries to limit China's control over itself, and uses a minor incident at Marco Polo Bridge to instigate a war to eat a chunk of China. However they neglected to fully mobilize the army at first, thinking that the Warlord of Shaanxi, Yan Xishan would refuse to rely on the government forces and only use his own, allowing easy victory. However they were shocked when not only did the Clique's army was better equipped then they thought, but when Peking fell, he relinquished control to Chiang.
It was thanks to an agreement between the two. Chiang would regain control, in exchange by making Yan the armaments minister, and equipping his personal units first with the new weapons. The Chinese forces were also bolstered with Yunnan and Ma forces, and made sure that the factories were moved inland in preparation They made sure to use the mountains that Taiyuan was in and the Yellow river as a defense line.
Usually this would be no issue for Japan. But dissonance between the Army, who suffered defeats that they didn't expect, and the Navy, who remained victorious on the sea against any pathetic attempt by the Chinese. Their bickering made sure to make it a land war, a war China was set to win.
This was particularly bad seeing that the Taiyuan Arsenal that Japan never was able to take gave the Chinese full ability to manufacture artillery and guns. This allowed them to build the European weapons, and as a result of their manpower now supplied with firearms, they seized and cut off the Kwangtung forces at Yantai and Erenhot. The dissolution of them effectively crippled the Japanese army. They couldn't stop the Chinese advance into Manchukuo.
The final death knell for the Kwangtung army was Puyi's abdication and dissolution of Manchukuo. While fighting bitterly to the end, the chinese forces wiped away any pockets left, and the road to Korea was opened. By seizing it, Hirohito forced his government to accept peace with Chiang. The terms include North China is given to China, Korea is made independent, and Formosa is given back to China. China will accept Japanese dominion over the Ryukyu Islands and Sakhalin. China's victory would lead to a lot of differences in WWII.