The immigrant visa process for many people involves a very long wait. Many people file immigrant visa petitions for their family members and end up waiting 10 or more years for an action on the petition. This is because there are annual limits on the numbers of visas available for most classes of prospective immigrants. Although the long waiting period is bad enough there are other problems that can arise and make the wait all for naught.
Many of the family-based immigrant visa preference classes depend on the marital status of the prospective immigration. For example, the 2b family sponsored preference is for unmarried sons and daughters of lawful permanent residents who are 21 or older. Currently, the waiting time for a prospective immigrant in this class is from 10 years to 18 years. A lot can happen in 10 years or more. One thing that happens a lot is that people get married. In a case involving a 2b class family member marriage will result in an automatic revocation of the visa if and when it is approved. The same result occurs for child in the 2a preference category.