In 562 Clovis II died after taking the throne at the young age of six he had grown into a competent king who had spread Frankish influence near and far. As was Merovingian tradition he split the throne between his sons Theuderic III his eldest son received Neustria, Chlothar III his middle son received Burgundy and Childeric II his eldest son received Astrasia. Chlothar convinced by his advisors tho take initiative decided to attack the lombards, as his fathers ally Perctarit had once again gotten deposed this tome by the duke of Benevento Grimoald* so with troops from Neustria sent by Theuderic III, Chrodbert (the Burgundian Mayor of the Palace) marched into Italy. Unfortunately Turin which had been straffing under Frankish rule had surrendered to the Lombards. In response Chrodbert sent a cavalry contingent from Neustria (that he didn't fully trust) to attack Vercelli which was a crucial junction between Pavia (the capital) and Turin. Grimoald sent a force to retake the city and the Neustrians fled in order to avoid a drawn out siege. Their leader Amalric decided to compensate by destroying some villages between Vercelli and Turin but this just made the local populace turn against the Franks and the cavalry had to return to the Frankish camp seeing the situation as bad Chrodbert decided to retreat back into Burgundy and wait out the winter or else be encircled in what was now hostile territory.
*In OTL he overthrew Perctarit in 671 but I want it to happen a bit earlier in order to start a war.
Edit: Sorry I have been away for so long
May our Clovis II rest in peace, you were a good ruler, even if sooner or later something must be done to settle the law of succession of the Franks ( because in the long run it is harmful to the "state" ) very interesting that the situation with the Lombards has once again led to a conflict between the two kingdoms, I sincerely hope that the Franks will be able through the Papacy ( at the time there was Pope Vitaliano ) to coordinate better with Costants II against the common enemy ( considering that in Otl he was already on his way towards the peninsula in 660, and that his most important campaign in Italy was in 663 against Benevento, and to increase his chances of victory he made an alliance with the Franks ), very curious to see the future developments of this war, hoping that in the end it will be a victory for the Roman alliance ( in the papal sense of the term ) and that perhaps a marriage will result between the descendants of Clovis II and the imperial court of Constantinople ( in particular if Constans II is not killed in 668, so to be able to have a daughter to marry in the land of Frankia )
to have a greater chance of hitting the Lombards from multiple directions at the same time, it would not be the case for the Franks to decide to personally control the Alpine passes ( therefore expanding their direct government into the old Roman provinces of Raetia and Noricum, today's Swabia and Bavaria - Austria ) furthermore with the surplus population they have compared to Otl ( thanks to the government of Clovis II who avoided the common intestinal wars between the constituent kingdoms of Frankia ) there would be everything in order to " Frankize " the regions beyond the Rhine to a greater extent than what happened historically ( also from a linguistic point of view, with a massive diffusion of neo-Romance dialects at a local level, assimilating the small Germanic populations on the border, considering that the Moselle region until the 13th century had a large, predominantly urban representation of speakers of the Romance dialect in Otl, it wouldn't be so strange in this TL to see the region remain with a stronger " Latin " majority ) yes, I know that it is a concept that I have already mentioned in a previous comment, but considering that thanks to these men more than Otl, some areas of Germany which historically were conquered definitively only after the seizure of power by Charles the Hammer and of his heirs, can be subjugated well in advance ( I am thinking of Friesland, already subject to important campaigns in TL, or of Western Saxony or Bavaria which here can be gradually incorporated into the Frankish system with more ease ) and this could potentially also give rise to a proto-Ostsiedlung process several centuries in advance ( since I imagine that the Saxons, to avoid clashes/strengthen themselves, will try to expand towards the East, conquering and integrating the local Slavic populations )