something that strongly influences later developments
seminal - important
Something ‘seminal’ is typically original and contains new ideas that have a profound impact on ideas, works, events. etc., that come after it. The word can also be used in relation to a person who has played a major role in the foundation or development of something. Most commonly used in written English.
Mark played a seminal role in the foundation of the organization. It would never have been conceived without him.
The prominent academic wrote the seminal book on the subject ten years ago.
In the future, I believe that people will look back at this time as a seminal moment in the history of the country.