While Romania was stepping up its domestic economic construction, Poland's war against Soviet Russia officially broke out.

On the Belarusian front, Polish troops launched an offensive on February 14 against Soviet troops along the Berezina River. The Polish army of 120,000 was attacking the Southwestern Front, which had 80,000 Soviet troops. At the same time, the Polish Third Army, bypassing the Romanian-occupied regions of Western Ukraine, attacked Kyiv. Pilsudski's dream of a two-seas federation remained unabandoned, but only to exclude the Romanian-occupied regions of Western Ukraine.

The Polish army went well in the early stage, not only conquering Minsk, the capital of Belarus, but also occupying Kiev. For a time, Poland's war intention to realize the largest territory of Poland was about to be realized.

In the face of Poland's attack, the Soviet Union also immediately dispatched troops.

By this time the Red Army had already defeated the White Army, Denikin had failed to retreat to the Crimean Peninsula to survive, and Romania had completely failed to seize the opportunity created for him. And on the Caucasus front, the Soviet Union has also advanced into mountainous areas. As for Kolchak in Siberia, he was completely defeated, and he himself was captured by the Soviet troops.

The opposition, which for a time was able to threaten the Soviet regime, no longer existed. At the same time, Russia signed peace treaties with Latvia and Estonia, and the threat of flanking was lifted.

Therefore, in the face of the Polish attack, Lenin and others sent Soviet Russian generals led by Tukhachevsky who grew up through the civil war. This genius general can be said to be very young at this time, born in 1893, even now he is only 27 years old.

Despite his youth, he has a lot of battlefield experience. Born into a decaying aristocratic family in the Dorogob district of the Smolensk province of Russia, he was studious and had a wide range of interests, especially in military affairs.

In 1911, he entered the First Armament School of Catherine in Moscow. The following year, he was selected for further studies at the Alexander Military Academy with the first place, and in 1914 he graduated and served in the Semenov Janissary Guard.

After the outbreak of World War I, Tukhachevsky went to the front with his troops and was captured by the Germans on February 19, 1915. He fled and returned to China in October 1917. After the outbreak of the August Revolution (formerly the October Revolution), Tukhachevsky was introduced to join the Soviet Red Army and the Communist Party, becoming the first former Tsarist Russian officer to join the Communist Party.

As soon as Tukhachevsky joined the Bolshevik Party, he was entrusted with the important task of going to the Eastern Front to take charge of the reorganization of the scattered troops and the preparation of the First Army of the Red Army. He completed the task brilliantly in a short time, and personally led his troops to victory over the White Guards several times.

He then appeared in various parts of the Civil War, both against Kolchak and Denikin, and his superior command skills helped him to win. And now in the face of the Polish attack, Lenin and others thought of him for the first time.

So in April, after he was appointed commander-in-chief, Tukhachevsky immediately transferred his troops. In the following month, the Russians concentrated more than 700,000 troops on the Polish front, while the Polish army was only 500,000 at this time. In terms of the comparison of forces, Soviet Russia already had an advantage. Although Poland is still conscripting, it is no longer possible for these troops to be on the battlefield now.

Even so, Tukhachevsky was still gathering troops. Why did he do that?

It turned out that Poland began a military campaign to demand "Russian-occupied lands" from Soviet Russia. This greatly offended the patriotism of Soviet Russia, and likewise hurt the passion and yearning for a "world revolution" that almost all the leaders of Soviet Russia cherished.

How could a Poland, which was regarded by the leaders of Soviet Russia as a "red bridge" to the world revolution, become a "thoroughfare" against Soviet Russia?

Thus, Polish patriotism collided with the patriotism of Soviet Russia. On April 29, the Central Committee of the Communist Party of Russia issued a proclamation calling on workers and peasants, "respected citizens of Russia" to rise up and defend the Soviet Republic.

For the first time, the Soviet power saw traditional Russian patriotism and the concept of Russia, which Lenin had criticized, as a weapon for winning the war against Poland, and under the banner of Russian patriotism, more than victory in the war against Poland was achieved.

A red Poland is in the interests of Soviet Russia, which is why Tukhachevsky still does not have enough troops. He wanted to establish Soviet power in Poland, because Poland was Germany at the crossroads of Europe after the past, and Lenin and others had their own ideas about the current turbulent Germany.

But while waiting for the rest of the forces to be assembled, Tukhachevsky will not do nothing.

The first Polish 1st Army Corps, located in the far north, was the first to suffer. At the end of May, the Russians counterattacked. The Polish 1st Army was defeated, and the Russian 15th Army recaptured the area between the Daugava and Berezina rivers.

On 24 May 1920, Polish troops in the south encountered for the first time the 1st Cavalry Army of Semyon Budyonny. On June 5, Budyonny broke through the Polish front with Cossack cavalry. The Russians then used mobile cavalry to strike at the rear of the Polish army, targeting communications and supplies.

By June 10, the Polish army had fully withdrawn, and on June 13 Kiev was abandoned.

At this time, the Polish army was already facing layers of oppression by the Soviet Russian Red Army, and Tukhachevsky was at this time several large armies, which put the Polish army in the White Russian region into a situation of taking care of one and the other. For a time, Poland was losing ground and losing all the territories it had previously seized.

At this time, Tukhachevsky still did not give Poland a chance to regroup, and led the army to continue to advance into the Polish hinterland.

Tukhachevsky launched an offensive along the Smolensk-Brest-Litovsk line on July 4, crossing the Ota and Berezina rivers. The 3rd Cavalry Corps in the north intended to move from the north to the border between Lithuania and East Prussia. The Fourth, Fifteenth, and Third Armies pressed westward, supported by the Sixteenth Army and Mozarska's Army in the south.

By 7 July, the Polish army was forced to retreat on all fronts.

However, due to the stubborn resistance of the Polish army, Tukhachevsky's plan to break through the Polish front and force the Polish army to the Pinsk swamp in the southwest failed.

At this time, the Soviet Russian army advanced almost 20 miles a day. Grodno in Belarus was lost on 19 July, and Brest-Litovsk was also occupied by Russian forces on 1 August.

At this time, the Poles realized that the Russians' goal was no longer limited to moving the border westward, and that Polish independence was in jeopardy.

At this time, the British government issued a "substantial" ultimatum to Soviet Russia, demanding that Russia cease hostilities against Poland and the Russian army (the White Army led by Wrangel in southern Russia). and the acceptance of the Curzon Line as a temporary border between Soviet Russia and Poland until the permanent border was negotiated and established. If Russia refused, Britain threatened to assist Poland in any way it could, but in reality Britain was also constrained by the domestic political situation.

On 17 July, Russia rejected the British ultimatum and counter-proposed to negotiate directly with Poland. Britain responded by suspending trade negotiations with Russia if it continued its attack on Poland, which Russia ignored.

In fact, at this time Poland had few allies. In 1919, France sent a 400-strong advisory group to Poland and assisted the "Blue Army", composed mainly of Poles and commanded by France during World War I, to reach Poland from France.

Hungary offered to send a cavalry corps of 30,000 men to support Poland, but Czechoslovakia refused to allow them to cross the border, although some trains loaded with weapons arrived in Poland from Hungary.

At this time, Poland looked at the only country that could help itself, and that was Romania, which had previously defeated Soviet Russia. At this time, in order to maintain its independent status, Poland asked for help from Britain and France on the one hand, and on the other hand, it also sent a delegation headed by Prime Minister Morachewski to Bucharest overnight to ask Romania for help. At the moment, the only one who can save them is Romania.

It should be mentioned here that at that time, in order to get to Bucharest as quickly as possible, Morachevsky flew directly to Romania on an unarmed plane. This was more than a decade before Chamberlain flew to Berlin peacefully, and Poland accidentally made history by becoming the first leader to fly on a business jet.