Here's why:
* Mutual intelligibility: Speakers of American English and other varieties of English (British, Australian, etc.) can generally understand each other. This is a key characteristic of dialects.
* Shared history: American English evolved from the English language spoken in Britain, with some changes over time due to isolation, influences from other languages, and regional variations.
* Gradual differences: While there are differences in pronunciation, vocabulary, grammar, and spelling between American English and other varieties, these differences are gradual and do not create a complete barrier to communication.
It's important to note that the distinction between a dialect and a language is often a matter of social and political factors, rather than purely linguistic ones. Some argue that American English is becoming so distinct from British English that it could eventually be considered a separate language. However, this is a complex issue and there is no clear consensus among linguists.
Ultimately, whether you consider American English a dialect or a language depends on your perspective and how you define these terms.