The link you posted says: "Sir Humphry made a bit of a mess of naming this new element, at first spelling it alumium (this was in 1807) then changing it to alu

The link you posted says: "Sir Humphry made a bit of a mess of naming this new element, at first spelling it alumium (this was in 1807) then changing it to aluminum, and finally settling on aluminium in 1812." To me it reads that British academics (Sir Humphry's peers) prefered the -ium spelling. It doesn't say they used political pressure to force him to change it. While the use of both spellings were in almost equal use in the general British and US populations for a long time, the article hypothesises that the -um spelling became dominant in the US because of Webster's -um entry.