U.S. bank card issuers (Visa, MC, etc.) routinely block ALL foreign transactions until you call their fraud prevention department to have them unblocked. Card-skimming is even more rampant in Europe than it is in the USA (although the USA is doing its darnedest to catch up).
- Try not to use an outdoor ATM. If you must, use one that is monitored by multiple CCTV cameras. If at all possible, use one in a bank lobby or secured ATM facility.
- Look over the ATM REALLY good for anything that looks out of place. Fake fronts, telltale signs of tampering, cameras pointing at the keypad, etc. BTW - having an ATM "eat" your card isn't something the card-skimmer (thief) did, they want you to keep using your card versus calling your bank to report it "lost." I actually witnessed the Florence Carabinieri shut down an ATM just off Piazza della Signoria because they found a suspicious device attached to it.
Read up on the State Department travel site about card skimming. Or, just google the subject.
I always take credit cards from two different banks and debit cards from two different accounts. Redundancy and back-up is aim here. I also don't use my debit for point of sale transactions or use my credit cards for ATM withdrawals.
If you card is declined, it is still possible to use it. But, you must call the fraud prevention department of the issuer and have a temporary exception made. This normally requires you to tell them the name of vender making the charge and the approximate amount. They will watch for this transaction - approve it - then close your card to further activity. It's a real pain, but it works. (Now you know why I carry back-up cards.) Having a cell phone with a local SIM comes in really handy here...
As Chip & Pin and Chip & Signature cards become the norm, card skimming will slowly fade away. Chip cards in Europe have reduced credit card fraud tremendously. The crooks are now targeting mainly foreign travelers who don't have chipped cards because their the easiest prey.
BTW - my MC "Chip & Signature" card works just fine as a "Chip & Pin" card in Italian vending machines when using the PIN issued by the bank. Just remember, it may take a bank 2 weeks or more to issue you, by mail, a PIN number and most banks treat the PIN as being unique to THAT chip (so it can't be changed without issuing a new card).