Which country was in charge of the early interactions between tribal nations and european nations?

 Tribal nations have been recognized as sovereign since their first interaction with European settlers. The United States continues to recognize this unique political status and relationship

The Roman Republic was a phase of the ancient Roman civilization characterized by a republican form of government. The republican period began with the overthrow of the Monarchy in 509 BC and lasted until its subversion, through a series of civil wars, into the Roman Empire. The precise date in which the Roman Republic changed into the Roman Empire is a matter of interpretation, with the dates of Julius Caesar's appointment as perpetual dictator (44 BC), the Battle of Actium (September 2, 31 BC), and the date which the Roman Senate granted Octavian the title "Augustus" (January 16, 27 BC), being some of the common choices. 
This is a distinction chiefly made by modern historians and not by the Romans of the time, however. The early Julio-Claudian emperors maintained that the res publica still existed under the protection of their extraordinary powers and would eventually return to its republican form. 
Inhabitants: Roman citizenship 
The Roman Republic had many different classes of people who existed within the state. Each one of them had differing rights, responsibilities, and status under Roman law. 
Government: 
Roman republican government was a complex system, which seems to have had several redundancies within it, and was based on custom and tradition, as much as it was on law.