In the states you need a professional (accredited) degree for licensure.  This is typically either a BArch (5 year programme typically) or an MArch (depending on previous undergraduate degree 2-3 years).  Courses are accredited through NAAB, not the AIA.  You should also be aware there is no direct reciprocity between the two systems, meaning your RIBA degree will not be recognized by NAAB and vice versa.

You can read more about the US system here:

http://www.ncarb.org/Studying-Architecture/Difference-Between-NAAB-Accredited-And-Non.aspx

Hope that helps!

"meaning your RIBA degree will not be recognized by NAAB and vice versa."

The statement above is not exactly correct; what is more accurate is that a RIBA degree will not be automatically considered by NCARB or the state board as having met the education standard, but you can have your RIBA degree evaluated by EESA - Evaluating Education Standards for Architects which is done thru NAAB.

https://www.eesa-naab.org/

I would also suggest you review NAAB - http://www.naab.org

Best.

@DocArchitecture

AIA does not offer degrees nor are they relevant to any person's ability to acquire a license to practice architecture in any of the States of America. The AIA is likely the most expensive magazine subscription you will ever have.

RIBA however, is more akin to NCARB...and between these 2 organization there is no longer a reciprocity agreement, so you would have to endure rigorous and excessive review processes which ultimately equate to "pay us a big fee" and we will license you.

Bear in mind, that not every State in the USA requires NCARB anything. You can meet their requirements by any number of means, but foreign education would certainly require an external evaluation for equivalency...and the license exam would be required in either nation.

To complete a B Arch architecture course (5 years) in the US your course will consist of a year and a half of general education courses that have to be unrelated to architecture. You will study 3 and a half years of architecture. 

The UK system has no general education requirement.

The US system is ruled by quantity- have you completed the necessary hours in each subject -it is an accreditation process. 

The UK system follows quality- therefore it is possible for a 5 year course to only be validated at Part I level ( what would normally be a 3 year UK course).- it is called validation. 

In the UK you gain a B Arch after 3 years ( Part I) complete a year of practice, and then an M arch after the next 2 ( Part II) at university, you then complete another year of experience and complete Part III, for registration with the ARB. 

In the US  a B Arch is a 5 year course, or you can study and unrelated course or a related course  as a BA or a BSc and then complete a MA in architecture.you then have a minimum of 3 years internship before sitting the registration exams for licensing.

A UK architect finds it hard to register as a US architect because they do not complete the general educational requirement at university level. An English A level exam pass is equal to an US High School AP course which counts as credit for university courses in the US but unfortunately cannot be considered in credit hour calculations for registration of foreign architects through ESSA at NCARB. The fact that you have studied design for 75 hours- 15 more than most US courses will not be considered. Similar differences and problems await US architects trying to become registered in the UK through ARB.

What architects actually learn in architecture school on both sides of the pond is remarkably similar. 

In both systems the accreditation/ validation boards stress professional studies in the learning outcomes but in reality approve schools who are have minimal professional education in their courses. In some US courses professional practice amounts to  only 3 credit hours out of 150 -160 credit hour course.  The UK system rectifies this omission in professional practice in the the Part III exam for registration, and the mandatory year out between Part I and Part II. I am not sure where it is rectified in the US system.

https://www.academia.edu/7038297/RIBA_Validation_or_NAAB_Accreditation-_A_comparison_of_architecture_education

@Architect with a suitcase the US system rectifies the professional practice issue by requiring you to complete the intern development program (IDP) in order to become licensed, which works out to around 3-4 years of categorized professional experience. See:

http://www.ncarb.org/experience-through-internships.aspx

The majority of the current  U.S. Architectural Registration Exam (ARE 4.0)  cover subjects that should have been taught and examined at an accredited school of architecture as these are  outlined in the NAAB/ NCARB  requirements and therefore should not need to be retested again.  I would love someone at NCARB to explain  why do you have to redo an exam on Structures, Schematic Design, Building Systems, Site Planning, and  Building Design and Construction Systems after years of going to university to study these?  If you are testing these subjects  then what is  the point of  NAAB courses?  Are they not being taught properly there? Why doesn't the  ARE  cover  the information you actually have to know as an architect but don't get taught in architecture school, like all the different types of  Law; How not to get sued; How to run a practice, (as a lot of people do); and ethics? The ARE is a standardized computer test where you sometimes have to choose an incorrect answer to pass, as the proposed answers are  not up to date with current building science. The vignettes are on a CAD program that is unique to the exams, and according to some blogs you have to have "errors" in your design in order to pass. http://www.shoegnome.com/2014/02/26/architecture-registration-examination-advice/ 

It will be interesting to see what happens as a result of the new American Board of Architecture. (http://architectboard.org/) who are proposing a new route for architecture students and registration.