The Shining Force makes it to Alterone after completing the third battle in the story.
To make things easier for you during the first few battles, there's two optional characters you can recruit:
Gong - At the start of the first battle, have your Hero retreat by trying to walk off the bottom edge. Once at the world map, go to the small house to the right of the Gate of the Ancients. Gong is on the left side of the house chopping wood.
Gort - After the second battle when back in Guardiana, go to the bar in the upper right corner of the town. Gort's fired up now and will join you.