Frankly, the US is the cause of this war, and they are the party that is receiving a lot of orders to buy weapons from allies in the world, so it can be said that the US is the most beneficial party. Besides, because of the war, the world fell into an economic crisis, also when they exported inflation to the countries that were their debtors.
The United States did not unleash this war and it is not the cause of it. It's all about the imperial ambitions of Putin, who wanted to go down in history as a collector of the lands of the former USSR, and possibly not only them, and the aggressive nature of the Russian mentality, which constantly needs aggressive wars to assert itself about the greatness of Russia. Also, one of the main reasons for Russia's attack on Ukraine is the desire to assign its history to Kievan Rus, starting from the 9th century, the fertile lands of Ukraine, a good industrial potential and hardworking Ukrainians. Without the history of Kievan Rus, the history of Russia looks very poor, even the territory of Moscow in the 13th century was the patrimony of one of the princes of this powerful state, and it turns out that Ukraine has the right to claim most of today's Russia, and not Russia to Ukraine. It even stole its name from Kievan Rus, because until the beginning of the 18th century it was called Muscovy or the Moscow kingdom.
Putin and his intelligence underestimated the professionalism of the Ukrainian army and the desire of its people for freedom and freedom. It was hoped that the resistance would be as flimsy as in 2014, when Russia first attacked Ukraine, seizing the Crimean peninsula, as well as part of the Donetsk and Luhansk regions. Therefore, on February 24, 2022, the Russian 200,000-strong invasion army was tasked to approach the outskirts of Kyiv on the same day by 15:00. The invaders have not fulfilled this task to this day. Now in Russia they say that Ukraine deceived them by pretending to be weak and defenseless. Strange justification for military aggression.
As for the benefits, the military weakening of Russia is certainly beneficial to the United States and other NATO countries. But even they underestimated the ability to defend Ukraine against Russia and gave Ukraine a maximum of seven days. That is why they did not give Ukraine heavy weapons on the eve of the attack, because they could have been seized by the Russian invaders. They gave only stingers and javelins for conducting guerrilla warfare under occupation. Help in more and more powerful weapons came from them only as the defeat of Russian troops in Ukraine and the brilliant conduct of military operations by the Armed Forces of Ukraine.
NATO has been preparing for a long time for a possible military confrontation with the USSR, and then with Russia. Now it is performing its main tasks with the hands of Ukrainians and they are amazed at how they are beating the "second army of the world", which all NATO countries were afraid of together.