Immediately after receiving his M.A. , MacMahon began teaching as an instructor in Columbia 's government department .
He received his B.A. from Columbia University in 1912 and his M.A. in 1913 .
Immediately after receiving his M.A. , MacMahon began teaching as an instructor in Columbia University 's government department .
He received his B.A. from Columbia University in 1912 and his M.A. in 1913 .