'Florian Geyer' was the German codeword to trigger preparations for the evacuation of the German civil population from the Reichsgau Wartheland, on each side of the Warthe (Warta) river, in German-occupied western Poland as the Soviet forces continued their westward advance (January 1945).

The Reichsgau Wartheland (initially Reichsgau Posen, sometimes called Warthegau) was a Nazi Reichsgau (administrative area) created from Polish territory annexed in 1939 after 'Weiss' (i). It comprised Greater Poland and adjacent areas, and only in part matched the area of the similarly named pre-Versailles Prussian province of Posen.

Most of this area had been annexed by Prussia from 1793 until 1807 as South Prussia. From 1815 to 1849, the territory was within the autonomous Grand Duchy of Posen, which was the Province of Posen until Poland was re-established in 1918/19 following World War I.

The area was inhabited by Poles and a German minority (16.7% of total population in 1921). During World War II 630,000 Poles and Jews were expelled from the territory into the occupied General Gouvernement (more than 70,000 from Poznań alone) in actions called the 'Kleine Planung'.

After the invasion of Poland, the conquered country was partitioned among four different Reichsgaue and the General Gouvernement area farther to the east. The Militärbezirk Posen was created in September 1939, and this was annexed by Germany as the Reichsgau Posen on 8 October 1939 with SS-Obergruppenfuhrer Arthur Greiser as its Gauleiter. The name Reichsgau Wartheland was introduced on 29 January 1940.

As in most Polish territories annexed by Germany, the Nazis' goal in the Wartheland was complete 'Germanisation' of the territory and its populace. This plan included the settlement of ethnic Germans from the Baltic and other regions on farms and other homes formerly occupied by Poles and Jews. By the end of 1940, 325,000 Poles and Jews from the Wartheland and the Polish 'corridor' had been driven into the General Gouvernement in a programme that saw most of those expelled lose most of their belongings. Deaths were numerous. In 1941, the Nazis expelled a further 45,000 people, and from the autumn of the same year began to kill the remaining Jews.

By the start of 1945 nearly half a million Volksdeutsche (ethnic Germans) had been resettled in the Gau. However, from the first days of 1945 the advancing Soviet forces drove the retreating Germans to the west through this and other regions. Most German residents fled to the west in 'Frundsberg' after thge issue of the 'Florian Geyer' warning phrase, many of them making the attempt too late, as a result of restrictions by the German regime, to escape the Soviets. It had been estimated that 50,000 of the former German residents died, some during their attempts to flee in dire winter conditions, some from the atrocities by the Soviets, and in revenge killing by Polish civilians.

Over the coming months, the remaining German population was expelled to Germany.