As the question title states, I need the crime data from all the united states. I can't find a dataset for that, only numerous small ones for the different cities and countrysides.
Is there such a united API or should I maintain these small ones as well ?
There is currently no single open dataset or API (Socrata maintained or otherwise) that covers the US completely. Many cities publish crime reports to their open data portals, but the coverage is still pretty sparse.
There's also the FBI Uniform Crime Reporting datasets, but those are aggregated at the city level (which again is somewhat sparse) and the most recent data is a partial update from the first half of 2015.