What is the main cause of high latency in a Web application?

The client's browser version can affect rendering and script execution speed but does not cause network-level propagation delay, which is determined by physical distance.

Latency is governed by propagation delay - the time required for a signal to travel the physical path between two endpoints - which increases directly with geographic distance. A greater distance between the client and web server raises the round-trip time (RTT), creating noticeable latency regardless of server processing speed or available bandwidth. This is the foundational reason content delivery networks place servers geographically closer to end users.

The number of CPUs on the web server affects server-side processing throughput but is not the main cause of end-to-end latency, which is dominated by the time data spends traveling the network path.

Large page object sizes increase the amount of data transferred and can reduce effective throughput, but this is a bandwidth constraint rather than the primary cause of latency, which specifically refers to round-trip signal delay.