Final answer:
Contingency theories are the leadership theories that consider external factors and the specific situation in determining the most effective leadership style.
Step-by-step explanation:
The group of leadership theories that argue that external factors help determine the best course of action for a leader are the Contingency theories. These theories suggest that there is no single best way to lead a team or organization because the most effective leadership style depends on the specific situation, including the nature of the task, the leader's personality, and the composition and preferences of the team.
Situational theories are similar but are specifically focused on the behavior of leaders and how it changes with the situation. Trait theories and Behavioral theories, in contrast, focus more on the intrinsic qualities of leaders and their behavior patterns, respectively, without placing as much emphasis on the external environment.