Proving historical assertions is very difficult. Some assertions can be proved by archaeological excavations, but many events are known because of testimony of witnesses (sources). Historians examine sources, consider bias, look for correlations and reinforcing evidence and construct a narrative that supports or contradicts the assertion.
Lack of proof is insufficient to assert that a sentence is false. Assertions can be unproven - not yet proven to be true or false. Many historical assertions remain under active debate and discussion; they are not yet proven. Additional evidence may arise, or historians may find new analytical methods that shift the balance towards or away from the assertion.
When answering question with the proof tag avoid speculation, and restrict the answer to events that are demonstrably proven.