You have Company Mo but it is just Company M. (with Mo people might think it is Missouri). Since he filed for a Pension in Kansas and in 1900 census he is at home in father's household in Neosho County KS, occupation "soldier" he probably enlisted in KS.
FYI: Spanish American War/Phillipine insurrection Pensions are included in the databases titled "Civil War Pension Index: General Index to Pension Files, 1861-1934" on Ancestry. It has Charles T Makemson filed in KS date: Feb 13th 1909 served M 40th U.S.Vol Inf. Note the Free LDS Family Search Beta website doesn't have the state filled in on their transcription.
Using Google search for 40th U.S. Infanrty below is the first result:
"Hazen, J.E. History and Roster of the 40th U.S. Volunteer Infantry. N.p.: 1901. [Library call number K/973.89/Pam. v. ]"
That is on the Kansas Historical Society website of "Military Records: Spanish-American War (1898) / Philippine Insurrection (1899-1901) Genealogical Resources"
"Item 4007 - Brief History of the U.S. Volunteer Regiments of the Philippine American War - A reprint of this rare article from The American Oldtimer magazine, printed in Manila in 1940. The article includes one paragraph histories of the following U.S. Volunteer regiments that served in the Philippines between 1899 and 1901:" Has 40th listed