Japan Summon

Japan one day suddenly materialises in another world. The Japanese government is put into chaos amid food shortages and many other issues. The JSDF is dispatched to survey the area and find out as much information as possible, the JSDF discover dragons during their search and men riding dragons. From this the Government confirms their beliefs the entire nation had been transported to another world. Negotiations between the government and their new neighbours swiftly begin in hopes of solving the food problem as quickly as possible. How were they transported here, why were they transported and what awaits the nation in this other world?