Footholds into enemy territories can be done as you grow in levels and should be completed before reaching Level 120. Take the time after completing your first zone to do your first foothold, or you can choose to complete one as soon as you gather your 100 War Resources which will prompt you to return to your mission table area where the first foothold quest can be obtained. Similar to how your initial zone selection was largely irrelevant, this selection is, as well. Simply pick one and complete it to earn your Mission Table second champion. Send your champions out on missions, recruit troops, and then head back out to quest in your second zone selection.