First of all. Let me make some basic assumptions. I will assume your world will consist of mostly ocean. I will also assume that there are many continents roughly the same size that we have on earth. That will mean an awefull lot of continents. Furthermore I will assume that your humans evolved on this world.
Evolution One light year means that on with a speed of 1km/h one would need 1 billion years to cross the planet. With this speed a species that reaches the other side of the world would have evolved into something completelly different by that time. 258
This speed would also mean that even if we assume life starts at one place by one billion years life would be everywhere.
Probably live would move to each continent separately, but nearby continent would influence one another.
Intelligence Intelligent life could evolve on many of these continent. But it would still be unlikely for two species to evolve to intelligence at exactly the same time on neighbouring continents.
Looking at human evolution it appears that we could not cross any oceans until quite late in our evolution. The americas where only settled 40000 years ago. That means that for most of its evolution sentient life will be bound to only a few continents.
Only after devoloping ships will people discover the other islands. Note that by that time the people will propably already have developed an advanced culture.
From there a culture can spread across the rest of the world at a relative slow speed. In our society it took only a few centuries from there to developing modern communication technology.
Effects This would mean that each civilization has a mother continent from where it originates. Politically people further away will become independent from their mother continent. However it would be unlikelly for them to lose all communication with their mother continent.
Some information of general interest (scientific for instance) could well spread very wide, but a lot of information will probably be only of local interest and people on other continent would not be interested in them. 335