Timelines, like the ones listed here, can help us see relationships between major world events and socio-cultural developments as they co-occur.
State Archives and historical societies often provide strong digital collections of primary source materials. Here are a couple of examples, but there are many more to explore online.
The historic 19th century periodicals listed here may all be found in the Bound Periodicals section of Memorial Library. The time range and topics-covered vary widely, but all pertain to the last few decades of the era.
A few key primary source collections:
Here are a few examples of significant collections of primary source materials that you can find on the open internet.