Will Muslims fight muslims in the Middle East?

Will this be a repetition of the religious wars in Europe centuries ago?

 

Iran is an islamic republic (shia muslims) with a population of more than 75.000.000.

Saudi Arabia has mostly Sunni muslims, only about 15 % shia muslims. Population about 30.000.000.

In an all out war the Saudis will definitely lose if they do not get military support by the USA.

More on http://www.theguardian.com/world/2016/jan/03/saudi-arabia-cuts-diplomatic-ties-with-iran-after-nimr-execution