Why did God wait so long to inform people about himself and why did he neglect to tell so many?

For example why didn't God tell the ancient American civilizations about himself? People like the Mayans, the Olmecs, the Incas, the Nascas and others? How about other parts of the world - What about the Ancient Sumerians? The ancient Egyptions? The Mesopotamians? There was no Monotheistic god, let alone a Jesus. How could these people be 'saved' and why did God not communicate His Word to them???