Which ruler briefly reunited the franks to fend off muslim invaders?

Charles Martel was Mayor of the Palace of the kingdom of Austrasia from the year 715 until his death in 741.

He is best remembered for having won the Battle of Poitiers in 732, traditionally considered the action that saved Europe from the Muslim expansionism that had already conquered the Iberian Peninsula; since then there were no Muslim invasions in the Frankish territories, and the victory of Charles Martel is considered decisive for medieval history in that it contained the Islamic expansion in the free borders.

the  seven  days  battles  were  a series of seven battles over seven  days from june 25 to july 1, 1862, near richmond, virginia,  during  the american civil war. the  seven  days ended with mcclellan's army in relative safety next to the james river, having suffered almost 16,000 casualtiesduring  the retreat.