Jacob had an angelic welcome on his return journey from his 20 years with Laban (see Jacob and Laban), a friendly, undefeatable force (that was also there when he had left i.e. Genesis 28:12) that may have encouraged Jacob to send word to his brother Esau that he was coming home.
"Jacob went on his way and the angels of God met him; and when Jacob saw them he said, "This is God's army!" So he called the name of that place Mahanaim.
The response was alarming. Jacob did the only two things that he could - disperse his group as much as possible, and pray.
"And the messengers returned to Jacob, saying, "We came to your brother Esau, and he is coming to meet you, and four hundred men with him."
While awaiting the encounter with his brother Esau, Jacob spent the night (almost) alone at the point that the attack would come, near the ford of the Jabbok River. He didn't get any sleep that night, not only because of apprehension of what the morning would bring, but because of one of the defining moments of Bible History and Prophecy that occurred there that night - Jacob's name change to Israel.
"And Jacob was left alone; and a man wrestled with him until the breaking of the day. When the man saw that he did not prevail against Jacob, he touched the hollow of his thigh; and Jacob's thigh was put out of joint as he wrestled with him. Then he said, "Let me go, for the day is breaking."
Genesis Chapter 33
When morning came, Jacob found himself standing alone against a force of 400 men. After again checking to see that he had done all that he could do for the safety of his family, he walked, alone, straight at the approaching army - very likely while thinking "I'm going to need Your help in a few seconds Lord...".
"And Jacob lifted up his eyes and looked, and behold, Esau was coming, and four hundred men with him. So he divided the children among Leah and Rachel and the two maids. And he put the maids with their children in front, then Leah with her children, and Rachel and Joseph last of all. He himself went on before them, bowing himself to the ground seven times, until he came near to his brother." (Genesis 33:1-3 RSV
Esau had either become more peaceful with age (which seems unlikely since he travelled with 400 troops) or he realized that The Lord was with Jacob and that an attack on Jacob would result in his own annihilation.
"But Esau ran to meet him, and embraced him, and fell on his neck and kissed him, and they wept." (Genesis 33:4 RSV)
Esau then invited Jacob to join him in his territory, in Seir (see the Fact Finder question below), but Jacob was no fool. Perhaps the invitation was genuine, but perhaps it was not. When the opportunity came, Jacob proceeded instead across the Jordan into "Israel."
"So Esau returned that day on his way to Seir.
Genesis Chapter 34
Of all of the recorded Children of Jacob, there was only one named daughter, Dinah. When their sister was treated wrongly, Jacob's sons responded with lethal force, despite Jacob's concern that it would trigger a war with the Canaanite people of the land who greatly outnumbered the Israelites.
"Now Dinah the daughter of Leah, whom she had borne to Jacob, went out to visit the women of the land; and when Shechem the son of Hamor the Hivite, the prince of the land, saw her, he seized her and lay with her and humbled her." (Genesis 31:1-2 RSV)
Fact Finder: What was Esau's claim to the land of Seir?