Question: In September 1939, when the Second World War begun, the then General Alfred Keller commanded the 4th Air Corps during the invasion of which countrty, he commanded Luftflotte 2, with his superior General Albert Kesselring, was a German "Luftwaffe Generalfeldmarschall" during World War II?

Context paragraphs:
Jagdfliegerführer Sizilien: Jagdfliegerführer Sizilien was part of Luftflotte 2 (Air Fleet 2), one of the primary divisions of the German Luftwaffe in World War II.  It was formed on April 5, 1943 in Trapani, subordinated to the II.  Fliegerkorps.  The command moved to Rome in July 1943, and was then known as Jagdfliegerführer Luftflotte 2.  The headquarters was located at Trapani and from July 1943 on in Rome.  The unit was disbanded in August, 1943.

24th Air Flotilla: The 24th Air Flotilla (第二十四航空戦隊, Dai-Nijūyon Kōkū-Sentai) was a combat aviation unit of the Imperial Japanese Navy (IJN) during the Pacific Campaign of World War II.  The flotilla, mainly consisting of land-based bombers, fighters, and flying boats, reported to the IJN's 4th Fleet.  As originally organized, the flotilla's core units were the 4th Air Corps, Yokohama Air Corps, and 1st Air Corps.

Jagdgeschwader 20: "Jagdgeschwader" 20 (JG 20) was a Luftwaffe fighter wing during the early phase of World War II in Europe.  JG 20 was founded on 15 July 1939 in Döberitz comprissed of one "Gruppe" and two "Staffeln".  A third "Staffel" was added on 5 November 1939 in Brandenburg-Briest.  The sole "Gruppe" was redesignated as 3rd "Gruppe" of Jagdgeschwader 51 (III. /JG 51) on 4 July 1940.  During the Battle of France it was subordinated to Luftflotte 2.  The unit's commanders included Hauptmann Hannes Trautloft, from 19 September 1939 to 4 July 1940.

Luftwaffe Order of Battle August 1940: For its Battle of Britain campaign against Great Britain during World War II, the German Luftwaffe had the following Order of Battle in the West. " Luftflotte 2" was responsible for the bombing of southeast England and the London area and based in the Pas-de-Calais area in France. " Luftflotte 3" targeted the West Country, Midlands, and northwest England, from bases a bit further north in France. " Luftflotte 5" targeted the north of England and Scotland, from bases in Norway. " Luftflotte 1" and "Luftflotte 4" were based in Germany, but most of their bomber formations had been reassigned to the three "Luftflotten" engaged in the Battle of Britain.  Some fighters were retained to provide air cover over Germany, however.

Jagdfliegerführer Oberitalien: Jagdfliegerführer Oberitalien (Fighter Leader Northern Italy) was part of Luftflotte 2 (Air Fleet 2), one of the primary divisions of the German Luftwaffe in World War II.  It was formed in July 1943 in Bologna and subordinated to the Luftflotte 2.  The headquarters were located at Bologna and moved to Pontecchio on March 18, 1944, moved again on July 15, 1944 to Verona.

Kurt Pflugbeil: Kurt Leopold Pflugbeil (9 May 1890 – 31 May 1955) was a German general (General der Flieger) in the Luftwaffe during World War II who commanded 4th Air Corps and Luftflotte 1.  He was a recipient of the Knight's Cross of the Iron Cross with Oak Leaves of Nazi Germany.

Alfred Keller: In September 1939, when the Second World War begun, the then General Alfred Keller commanded the 4th Air Corps during the invasion of Poland, assuming this command on 13 October 1939.  The following campaigns, during campaigns against Norway, the Netherlands, Belgium and the Battle of France, he commanded Luftflotte 2 with General Albert Kesselring as his superior.

9th Air Division (Germany): 9.  Flieger-Division (9th Air Division) was one of the primary divisions of the German Luftwaffe in World War II.  The division was founded on 1 February 1940 in Jever and initially subordinated to the Oberkommando der Luftwaffe (OBdL).  On 23 May 1940 the division was subordinated to the Luftflotte 2 and transferred to Soesterberg in July 1940.  The unit was redesignated "IX.  Fliegerkorps" in November 1940.

Albert Kesselring: Albert Kesselring (30 November 1885 – 16 July 1960) was a German "Luftwaffe Generalfeldmarschall" during World War II.  In a military career that spanned both World Wars, Kesselring became one of Nazi Germany's most skilful commanders, and one of the most highly decorated, being one of 27 soldiers awarded the Knight's Cross of the Iron Cross with Oak Leaves, Swords and Diamonds.  Nicknamed "Smiling Albert" by the Allies and "Uncle Albert" by his troops, he was one of the most popular generals of World War II with the rank and file.

Helmuth Förster: Helmuth Förster (19 April 1889 – 7 April 1965) was a German general' in the Luftwaffe during World War II.  A decorated World War I aviator, he returned to military service in 1934 as an "Oberstleutnant" in the Luftwaffe.  Promoted to "Oberst" in 1936, he was appointed to command the 4th Bomber Wing.  During the invasion of Poland, Förster commanded the "Lehrdivision" with significant success.  He was then appointed as chief of staff of the 5th Air Fleet during the invasion of Norway.  After serving on the German-French Peace Commission, he was appointed as military governor of the German-occupied territory of Serbia from April to June 1941, then commanded the 1st Air Corps during the invasion of the Soviet Union until October 1942.  Whilst in command of the 1st Air Corps he was awarded the Knight's Cross of the Iron Cross.  He spent the remainder of the war as chief of administration at the Reich Ministry of Aviation.  He was pensioned as an "Oberstleutnant" in 1952.

Supporting paragraphs: Alfred Keller Albert Kesselring
Answer: Poland