The bird and the tree are friends．The bird often sings songs in the tree．Autumn comes．The bird has to fly to the south．Spring comes.The bird comes back，but she can’t see the tree．Grass tell her some workers cut the tree down and took him to a factory．Then the bird flies to the factory．The workers told her they cut the tree into wood．They used the wood to make matches．Then they took the matches to a village．The bird flies to the village and sees a girl used the last match to make the fire．The bird sings a sad song to the fire．

新航路开辟后，世界各民族的历史逐渐融合为一部统一的人类历史。这种“融合”和“统一”实现的主要途径是（   ）