Cantonese vs Mandarine

http://www.zgyyzx.com/1.

why Cantonese is not a language but a dialect of Chinese?

http://chinese.stackexchange.com/questions/2858/why-cantonese-is-considered-as-a-dialect-of-chinese

they're not completely different, but similar in some ways. You should know, all dialects are different.

• Mandarin Chinese is not a natural language. It grabs pronunciation from Beijing dialect, vocabulary from all the northern dialects, grammar from the articles written by great writers during the New Culture Movement.
• Modern dialects have only one root -- Middle Chinese. Middle Chinese (中古漢語) is the lineal descendant of Old Chinese (上古漢語). Cantonese is also from Middle Chinese.
• Although the written form is different. The original characters are the same. The new characters are only made to show the pronunciation of Cantonese.
• Northern dialects of Chinese lost the entering tone (入聲). For example, 力 is pronounced as "li4" today in Mandarin, but it's "lik" in Middle Chinese. Many southern dialects still have entering tone.
• Cantonese is not the same as Middle Chinese, but a descendant. In fact, all today's dialects are its descendants.

You see: Cantonese is from a language which all other dialects (including Mandarin) are from, so Cantonese is a dialect of Chinese, not a new language.