Becoming the only king on all lands is your task in One King World. It is quite ambitious, but quite feasible if you use the right strategy. To start the conquest and capture of neighboring kingdoms, you need to make your country strong both economically and militarily. Develop the economy and it will be aimed at creating the strongest army. Do whatever is necessary to replenish and strengthen it. When you're ready, choose a kingdom and attack it. You should first hover over the selected territories and carefully read the information that appears so as not to get into a mess in One King World.