Why did the Spanish Civil War end in the defeat of the Popular Front?

The Spanish Civil War began in 1936. At this time, fascist parties already existed in Germany and Italy. In Spain, the Popular Front won the parliamentary elections. But General Franco, who launched an offensive on the Popular Front, did not accept this. So, until 1939, wars between the fascist bloc and anti-fascist associations were waged in Spain. But in the end, the Civil War was resolved by the victory of General Franco. After that, a totalitarian regime was established in the country under the command of Franco.