In February 2022, Russia invaded Ukraine, escalating the Russo-Ukraininan War and embroiling Europe in its largest conflict since World War Two. Russia's actions were condemned almost universally by the world, with 141 of the United Nations Assembly's 193 members voting to reprimand Russia and demand it cease hostilities, 35 members (including China) abstaining, and 5 (including Russia and Belarus) voting against the reprimand. While Russia sought to topple Ukraine relatively quickly (and apparently expected to do so), Ukraine, aided by significant amounts of aid from NATO and other countries, was able to withstand the initial blow and turn the conflict into an extended operation. From the start of the invasion to October 2023, Ukraine has actually inflicted greater losses of troops and equipment upon Russia than vice-versa.
As of October 2023, the only country that has been proven to have sent troops to Ukraine is Russia, whose troops were sent to not to assist Ukraine, but to invade it. Many NATO countries have sent military and humanitarian aid, but as of October 2023 none had sent actual troops. Close Russian ally Belarus, which has allowed Russia to place troops and missile launchers in Belarusan territory and had amassed its own troops along the Belarus/Ukraine border, has been accused of covertly sent troops into Ukraine to fight alongside Russian troops. However, Belarusan president Aleksander Lukashenko has denied this and repeatedly claimed Belarus would not send troops to attack Ukraine unless Ukraine attacked first.
Although NATO has not sent soldiers into Ukraine, several NATO countries have sent sending military aid. The largest backer of Ukraine is easily the United States, which has sent billions of dollars in military equipment to Ukraine itself. In addition, other NATO countries including the United Kingdom, France, Germany, the Netherlands, and Canada have sent support to Ukraine. Moreover, several countries in Asia and Oceania, such as Japan, South Korea, and Australia have come out in support of Ukraine. A number of Asian countries that are traditionally allied with Russia, such as China and North Korea, have largely stayed out of the conflict.
The Ukrainian government has repeatedly demanded stronger support from NATO. Thus far, NATO member countries have sent significant amounts of weapons, ammo, and other aid. However, NATO has declined to contribute actual troops for fear that such an action could trigger China, Iran, and/or Belarus to offer troop reinforcements for Russia and cause the conflict to spread to additional countries, even to the point of escalating into World War Three.