Essentials/Need to know
| commas in introductions | use commas to separate introductory elements from the main sentence | In 1865, the Civil War ended. When the Civil War ended in 1865, northern photographers extensively documented the fallen Confederate strongholds. | Comma is optional with small elements. Comma is required with adverb clauses. Remember: A comma is never wrong when used with introductory elements. |
“You’re never wrong if you do use a comma after an introductory element.”