Here's a list of Big Ten National Champs between 1933 and 1960:
1933 - Michigan (retroactive)
1934 - Minnesota (AP)
1935 - Minnesota (UP)
1936 - Minnesota (AP)
1940 - Minnesota (AP)
1941 - Minnesota (AP)
1942 - Ohio State (AP)
1944 - Ohio State ("civilian")
1947 - Michigan (retroactive)
1948 - Michigan (AP)
1954 - Ohio State (AP)
1957 - Ohio State (UP, FW)
1960 - Minnesota (AP, UPI)
In a 28-year span, that's 8 consenus national champs (1934, 1935, 1936, 1940, 1941, 1942, 1948, 1960); 2 split champs (1954, 1957); 2 retroactive champs (1933, 1947); and one minor champ (1944). Add in NC's for Notre Dame in 1930, 1943, 1946, 1947, 1949, and 1953, plus Michigan State in 1952, and the 1930's, 40's, and 50's were clearly the Golden Age of midwestern football. Now, not so much....