Land fighting started on September 8, when the first German armored units reached the Wola district and south-western suburbs of the city.

[1]: 78 From the very first hours of World War II, Warsaw, the capital of Poland, was a target of an unrestricted aerial bombardment campaign initiated by the German Luftwaffe, which was controlled by Hermann Göring.

Apart from the military facilities such as infantry barracks and the Okęcie airport and aircraft factory, the German pilots also targeted civilian facilities such as water works, hospitals, market places and schools, which resulted in heavy human casualties that possibly led to the early surrender by lowering of morale of the Polish army defending the city.

The latter was composed mostly of fire-fighter brigades and volunteers and was supervised by Colonel Tadeusz Bogdanowicz and Julian Kulski, the deputy president.

However, the brigade also suffered heavy losses, and by September 7 it had lost over 38 pieces of equipment, or approximately 70% of its initial strength, which greatly contributed to an early surrender.

Furthermore, as the war progressed, the German high command redirected more bombers to attack the city, especially the historical old town, the Warsaw Royal Castle and other iconic monuments, significant to the Polish nation and its capital.

On September 3, the forces of German 4th Panzer Division under Major General Georg-Hans Reinhardt managed to break through positions of the Polish Łódź Army near Częstochowa and started their march towards the river Vistula and Warsaw.

General Walerian Czuma, the head of the Border Guard (Straż Graniczna), became its commander and Colonel Tadeusz Tomaszewski its Chief of Staff.

Gradually, the forces of General Walerian Czuma were reinforced with volunteers composed of mostly civilians, including women and children, as well as rearguard troops and units withdrawing from the front.

On the morning of September 8, the suburbs of Grójec, Radziejowice, Nadarzyn, Raszyn and Piaseczno were captured by forces of German XVI Panzer Corps.

The well-placed Polish 75 mm anti-tank guns firing at point-blank range, and the barricades erected on main streets, successfully managed to repel all initiated assaults and unexpected attacks.

On September 8 the Commander-in-Chief, Marshal Edward Rydz-Śmigły ordered the creation of an improvised Warsaw Army (Armia Warszawa) under General Juliusz Rómmel.

As a result of this offensive that later became known as the Battle of Bzura, German commanders withdrew the 4th Panzer Division and sent it to counter the Polish threat near Kutno.

On September 11 the Polish Commander in Chief ordered that Warsaw was to be defended at all costs, despite the possible heavy casualties and civilian losses.

The following day the forces of German 3rd Army (under General Georg von Küchler) broke through Polish lines along the Narew river and started its march southwards to cut off Warsaw from the east.

It was assaulted by cavalry units under Władysław Anders, but after heavy fighting the Polish counter-offensive failed and the forces were withdrawn to the south.

Other Polish units fighting under General Juliusz Zulauf near the Narew River area retreated and reached Warsaw on September 14.

Constant bombardment of civilian facilities, lack of food and medical supplies resulted in heavy casualties among the city's population.

The Soviet Union's entry into the war and lack of support from the Western Allies made the defence of the city pointless and heavily demotivated the volunteers in participating in any further military actions.

Several units declined to put down their weapons and cease fire, and their commanding officers had to be visited by generals Czuma and Rómmel personally.