American Allowance in Schengen Area vs Having a Schengen Visa in Schengen area

Question

I am aware of the 90/180 rule of the Schengen agreement stating that one in possession of a Schengen visa can only stay in the Shengen area (regardless of which country it is) for 90 days in any 180-day period. I am an American citizen and as such I believe that I do not need a Schengen visa to enter any of the countries comprising the Schengen agreement. That being said, I am still limited to a 90-day stay in whatever country it is, just like those who have a Schengen visa. However, this is my question:

I'm not sure if that allowance for an American citizen of a 90-day stay is unique to the country in which I am staying OR if it applies to the entire Schengen area just like the Schengen visa. For example: would I be able to enter, say, France (which is a part of the Schengen area) for a maximum of 90 days, and then travel to Germany (which is also a part of the Schengen area) for a new 90-day period?

This of course would not be possible with a Schengen visa, because the Schengen area is basically acting as a united country as far as the Schengen visa is concerned. Is this the same for the American allowance of a 90 day stay? Or can I stay in the individual countries for periods of 90 days?

Answer 1

Same rules apply for Americans or other nationals who do not require a visa. Once you enter any Schengen member state, the counter will start counting the 90 out 180 days.

From The European Commission official website

As from 18 October 2013 for the vast majority of the third-country nationals – irrespective of being visa required or exempt – who intend to travel to the Schengen area for a short stay (contrary to reside in one of the Member States for longer than 3 months) the maximum duration of authorised stay is defined as "90 days in any 180-day period […]". "The date of entry shall be considered as the first day of stay on the territory of the Member States and the date of exit shall be considered as the last day of stay on the territory of the Member States

Answer 2

As far as Schengen rules are concerned, it makes absolutely no difference, as @MeNoTalk already explained. Everything you read about the 90/180 rule for visa holders fully applies to you as well.

Interestingly, there is no separate set of rules for people who don't need a visa. The visa requirement is created by a single line in article 5 of the Schengen Borders Code on “entry conditions for third-country nationals”.

(b) they are in possession of a valid visa, if required pursuant to Council Regulation (EC) No 539/2001 of 15 March 2001 listing the third countries whose nationals must be in possession of visas when crossing the external borders and those whose nationals are exempt from that requirement, except where they hold a valid residence permit or a valid long-stay visa;

The rest of article (including the rules about travel documents, purpose of stay, means of subsistence, maximum stay, etc.) fully applies whether you need a visa or not.

Note that your not requiring a visa for short stays also directly stems from this provision in the regulation. Individual Schengen countries are not free to impose additional restrictions (Poland could be tempted because unlike other Schengen member states, they are still not covered by the US Visa waiver program), except when they are explicitly allowed to do so by the regulation (that's the case for airport transit visas).

Additionally, there are some funky rules based on earlier bilateral agreements (especially between Australia and some Schengen countries) and on the visa facilitation agreements mentioned by @cpast but all that is moot for US citizens.