Western Allies and Axis compared
It's often argued that the Western Allies enjoyed a superiority in economic/industrial resources. Well, let's see if that's actually true by first comparing the GDPs of the territories under control of each coalition assuming the USSR (and Finland) is (are) never involved in the war.
GDPs of the territories of each coalition, levels of 1939 measured in millions of 1990 dollars:
Axis --------------------- 1,222,815
----- Germany ----------- 428,750
----- France -------------- 200,840
----- Japan --------------- 166,506
----- Italy ---------------- 154,470
----- Poland --------------- 67,788
----- Netherlands --------- 48,687
----- Belgium ------------- 43,216
----- Czechoslovakia ----- 31,578
----- Hungary ------------- 26,184
----- Denmark ------------ 22,803
----- Greece -------------- 18,875
----- Norway -------------- 13,118
Western Allies --------- 1,269,990
------- USA --------------- 862,995
------- UK ---------------- 300,539
-------- Canada ----------- 55,167
-------- Australia --------- 40,749
-------- New Zealand ---- 10,510
I am not including Yugoslavia, Romania, Bulgaria, China, India, Thailand other British, French, Dutch and Japanese colonies which were all agricultural near-subsistence economies of negligible war-making potential and hence strategically irrelevant in industrial terms.
Also, if we take in consideration that the US was in the Great Depression (although the same was true for many European economies under the Axis sphere of power, like France, Netherlands, Belgium, whose per capita incomes did not grow like the US's between 1928 and 1939), the US's economic potential was greater than 863 billion, adjusting for an increased labor supply of 25% or increasing per capita income to long run growth trend levels yields a GDP of about 990 billion, increasing the Allied total to ca. 1,400 billion, still that's only 15% bigger than the Axis total.
Overall, though, I see coalitions with relatively similar aggregate economic size. Although the territories inside the Axis sphere of power had greater populations of over 300 million compared to 200 million for the Anglo-Saxon countries, also greater stocks of industrial machinery (Germany alone had a bigger stock of machine tools than the US) and produced more Nobel prize winners in the decades before WW2.
Overall, it's a popular myth the idea that the Western Allies enjoyed enormous superiority in potential industrial resources. However, during the war it's true the Western Allies military expenditures were a bit bigger, for 1944, they spent about 74 billion in 1939 dollars compared to 60 billion for the Axis, for the 1940-44 period as a whole, it was ca. 240 billion to ca. 210 billion (still quite closer than most would think):
That's because the economies of France, Netherlands, Belgium and Denmark collapsed by 40% following German invasion, that was a decrease of 124 billion or 10% of the Axis' total GDP, adjusting US GDP up for correcting for the depression we have that in the German sphere of power economic potential was relatively 1,100 billion to the Western allies 1,400 billion, a ratio 1.3 to 1. That fits pretty well with the a ratio of 1.25 to 1 in military expenditures in 1944. Although Japan alone was 20% of Axis military expenditures in 1944, even though it was ca. 14% of the 1939 Axis' GDP.
"In tactics, as in strategy, superiority in numbers is the most common element of victory." - Carl von Clausewitz