Historical understanding is built on

your list doesn't mention any of them at all.

and what does "these" mean anyway ?

norsemen from northern countries had made earlier journeys

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.

try only asking one question