How was japan able to defeat both china and russia during their expansion into asia ?

Japan, Russia, and China were countries that were in different situations. Japan was rapidly strengthening in every aspect, especially military and economically. Also, Japan was stable politically and united. China and Russia were different stories. China was divided into two fractions which were constantly fighting between each other. It was not united by any means, and the country was weak economically and military. Russia was facing big internal turmoil, with its economy suffering in meantime, division between the population, and change of power. Japan used this opportunity, and it managed to defeat both of these countries in military conflicts, despite it having much smaller population, much smaller territory, and almost none natural resources of its won.