Summary
Path dependence is the idea that where a system can go next is limited by the route it has already taken: early events or choices get locked in and shape what follows. Economists developed it to explain why technologies and standards persist. The stock example is the QWERTY keyboard, which the economist Paul David used in 1985 to argue that an inferior standard can survive on the legacy it has built up.
The mechanism is self-reinforcement: the more a choice is made, the greater its benefits, so switching gets harder. Political scientists apply it to institutions, where Kathleen Thelen has called it both too contingent and too deterministic.
Rationale
Part 2 asks “What holds the current contexts in place”. One answer is here: arrangements that reinforce themselves. To accident we’d add power, since they’re “often backed by significant disparities in power and resources”.