If you had one ticket to LAX (one PNR) and another for the US domestic flights (another PNR) that is how it works when the first flight is delayed and you miss your connection. Technically the US domestic airline considered you as a no show because you did not board your first domestic flight, that would have essentially been the start of your US-domestic ticket.
One would have the same problem if flying from LAX to EWR with a change of plane and new ticket at DFW. If you missed the connection at DFW the airlines do not know anything except you were a no show and they have no responsibility. Booking the same itinerary on a single ticket (eg one PNR) and the airline is obligated to get you there. It works the same everywhere.
If all of your flights were on the same ticket the airline would have owned the problem and had responsibility to get you to your destination as timely as possible.
That is a common exclusion. Not meaning to be harsh, but buying an international ticket expecting the flight to be on time for a connection is only one delay - you could be in customs-immigration for 15 minutes or 3 hours, and you can arrive on time but still miss a connection because of that.
I cannot offer you hope that the travel agent will accept responsibility unless they sold you both tickets.
FWIW I often use multiple tickets, but always assure a minimum of 4 hours and often an overnight at the transfer point, just in case. International flight delays up to 6 hours are common, but much longer rare, although cancellation happen. I play the odds. Since your flight was cancelled I presume they rebooked you on the next available so it would probably come under ‘rescheduling’.
