Answer by A Quora admin:
I am not sure if your question is am I engaged in interstate commerce or do I need to register in another state if I have an office or physical location there. Interstate commerce is generally defined as shipping tangible goods across state lines and really has no relevance to where you have an office, but rather how you conduct your business.
You could have only one physical location in one state, but ship goods everywhere and thus be engaged interstate commerce.
Having a physical location or operation in more than one state will most certainly create nexus in every state where you have such physical presence and would by extension require you to have registered as doing business and have a registered agent in each state where you are located. For most states just having one employee with or without an office or storing inventory in the state will create a need to register with the state. I have even seen a situation where having no employees, no office and no inventory, but having a car parked at the airport for a traveling salesman to use created nexus and thus required the business to register and pay taxes in the state where the car was parked.