unusual capital gain tax question

[jc2002]

I opened an etrade account while I was not a US tax resident 7 years ago. I bought some stocks and kept them in the account. Last year, I became a US tax resident. I also sold some shares and made some profit. Now I need to report tax on these gains.

My question is: is the gain considered taxable since when I bought the shares, I was not a US resident? anywhere I can check on such info?

thanks.