"Of course" is only correct as two words. "Of" is a preposition modifying the noun "course". Google Ngram Viewer shows it's most popular spelling choice. "Ofcourse" is never mentioned in dictionaries
"Traveled" is correct spelling in American English. Final consonant doubled only in stressed syllables. Exception: "kidnaped" can be spelled "kidnapped"
Labor and labour are two different spellings for the same noun. American English uses "labor," British English uses "labour". Both spellings are correct when preceded by an adjective
Both "canceled" and "cancelled" are acceptable in American English. "Canceled" is more common than "cancelled". "Canceling" is more common than "cancelling"
American and British English have different spelling conventions. Silent -e is typically dropped with suffixes in American English. British English retains silent -e in some words
Americans and British English historically had different linguistic approaches. This linguistic movement created words with identical meanings