Here's what we know:
* First recorded usage: The first recorded use of "malarkey" in English was in 1918, appearing in a US Army newspaper.
* Irish connection: The word is thought to be derived from the Irish word "malairt" (pronounced "malart") which means "change" or "alteration."
* Evolution of meaning: "Malairt" evolved into "malarkey" and came to mean "nonsense" or "worthless talk" likely due to its association with political changes and rhetoric.
So, while the precise origin is unclear, the Irish language is strongly suspected to be the source of "malarkey."