The Native Americans had an immigration problem a few hundred years ago. They had lax border controls, especially on the East Coast.
The immagrants first arrived in small number, but gradually,over the decades, their numbers increases as more flooded in.
The country's morals declined, crime increased, polution increased, envioronmental damage increased, and, eventually the immagrants took over control of everything!!
The Persians were not Muslim, as this faith was not founded until 800 AD. The Persian Wars were over a mellienia before then.
The Spartans aren't the only small body of men to hold up a vast army in history.
In 1941, 6 men in a KV2 "Land Dreadnaught" heavy tank , sat on a hill and held up 2 German divisions for 3 days. It took seven 88mm. gun hits to finish them,as previosu attempts with 50mm. and 37mm. anti-tank and tank guns over the previous days had failed to even scratch the armour.
Ironically, if they'd held out just another 4 hours, the Russian would have been able to defeat the German invasions throughca counter attack from a strong position. however the Germans occupied this position and the attack never happened.
The event was in the first few days of the invasion. We were taught this as an example, in the Army, of how sometimes, idividuals or a small group, realising that they are in a key position, can change the course of a war if they make the right informed decissions.
These 6 men nearly came close to changing history by just 4 hours!!
I remember the old 1960's Spartan film. The traitor led some of the Persians, via a mountain pass, to attack the Spartans from behind, cuttingv off their escape route.