Q: I want to change my country/app store; but when I put my payment information in, it keeps saying my card is declined. How do I fix this?? I really want to change my region/app store!

If you owe iTunes anything, or if you had any outstanding passes (buying a pass allows you to download a TV series as/when its episodes are released), you would get a different error.

You are currently in the US, the card was issued by a US bank, and it's registered to the same name and address as you are trying to put on your account ? If you are, and the card is, then try contacting your card issuer and see if they are declining it. If they aren't then do you have a different card that you could try ?

I am having the exact problem as op, but I don't have a card issued by a US bank. Is that a must to change app store region? I can and have used my credit cards to purchase things from the US even though my cards are not issued by a US bank. So why is apple declining my cards?

Are you in the US ? If you aren't then you cannot use the US store - being in a country is part of the store's terms

Is that a must to change app store region?

It seems to be now : Why can’t I select None when I edit my Apple ID payment information? - Apple Support

When you change the country or region of an existing Apple ID, you must provide a payment method and update your billing options. If you want to remove your payment method after you change the country or region, you can change your payment information to None.

I can and have used my credit cards to purchase things from the US even though my cards are not issued by a US bank. So why is apple declining my cards?

Different stores have different rules/validation, asking for card details is way of checking that you have valid billing address in the country

ugh I see, thanks for the clarification