What happens after the citizenship app is filed, and why is the residency requirement different for those married to US citizens

After an application for naturalization is filed, the applicant will be scheduled for a biometrics appointment. USCIS will conduct background checks on the applicant and send the case to the local field office for an interview. During the interview, the applicant will be administered the English and civics test as well as questions related to eligibility. If all goes well, the application will be approved and the applicant will be scheduled for an oath ceremony.  The residence requirements are different for spouses of United States citizen, because the law provides a quicker path to naturalization as an additional benefit of being married to a U.S. citizen.  You can read more about naturalization at http://myattorneyusa.com/how-to-get-naturalized-in-the-united-states.