Recently, I've engaged in discussions about WB's power level, the Marineford war and all that and one thing that I seem to be the only one thinking is that, were Sengoku willing to keep going and were their entire force to be available (Mihawk not leaving,for example), they would take down Shanks as well (with big casualties though).
If you don't agree,lets just see what the two sides (Whitebeard vs Marines) were playing with:
WB's side:
-WB himself (died and achieved nothing by himself)
-Marco (was easily handcuffed and was mostly useless)
-Jozu (was able to make Aokiji busy but ended up being defeated without giving much of a fight)
-Vista (was able to maintain Mihawk busy for a while but did nothing special. His atatcks were literally ignored by Akainu)
-Ace (at some point of the war) (Died)
-Remaining of his crew which was not relevant at all in the war despite being too hyped
-43 well known New World crews
-Luffy (did most of the relevant work)
-Crocodile (was really helpful,saved Ace and saved Jinbe and Luffy)
-Ivankov (was jumping and dancing throughout the battlefield but didn't achieve anything at all)
-Jinbe
-Impel Down Escapees
-Buggy
-Boa Hancock ended up helping them as well
Marines' side:
-Garp (untouched)
-Sengoku (untouched)
-Akainu (the only marine to be damaged but it wasn't that big a deal,didn't slow him down at all)
-Kizaru (was kicked by Marco once but even Marco said it was nothing. So untouched as well)
-Aokiji (barely damaged by Jozu) (nearly untouched)
-Mihawk (untouched)
-Doflamingo (untouched)
-Kuma (barely damaged due to armor)
-100.000 elite soldiers
-All Vice Admirals
-The remaining Shichibukai
So,as you see, the Marines were pretty much perfect in this war while Whitebeard struggled a lot. The only mission of WB's was to save Ace and he wouldn't have been able to do so without the surprise allies that showed up (Luffy, Jinbe, Crocodile).
And after this,Shanks appears with his crew and the war stops and people assume it was because they fear Shanks when the man they call the strongest man in the world is dead right there and has been killed 5 minutes ago??? Are you kidding me?
The first thing Shanks said was for Marco to stop encouraging the fight and to withdraw from there. Then he told he would fight anyone who wanted to keep fighting. Shanks said he wanted to give WB and Ace a proper burial and Sengoku, knowing his goal had been achieved and knowing this new war would claim many lives pointlessly, decided to call of the war.
It is all right there. If there's one person that was afraid of Shanks,that one person was Blackbeard who decided to run away. The marines were ready for round 2.
Of course,fighting these guys would not be easy but it would not be that hard neither
But I believe that the Marines had enough forces to do so brilliantly and get started on even a third Yonko
Do you agree?