The book begins as follows - "Now it came to pass, in the days when the judges ruled, that there was a famine in the land. And a certain man of Bethlehem, Judah, went to dwell in the country of Moab, he and his wife and his two sons. The name of the man was Elimelech, the name of his wife was Naomi, and the names of his two sons were Mahlon and Chilion--Ephrathites of Bethlehem, Judah. And they went to the country of Moab and remained there. Then Elimelech, Naomi's husband, died; and she was left, and her two sons. Now they took wives of the women of Moab: the name of the one was Orpah, and the name of the other Ruth. And they dwelt there about ten years. Then both Mahlon and Chilion also died; so the woman survived her two sons and her husband" (Ruth 1:1-5).
Bethlehem (in the territory of Judah) was typically known to be very fertile land. Interestingly, the text doesn't indicate the specific cause of the famine. The natural assumption would be that a drought had afflicted the region harshly, and even the areas known for good crop production were struggling. However, it could very well be the case that this famine was not inflicted by the weather but by the Midianites (cf. Jud. 6). The author indicates that the narrative took place during the period of the judges which makes this view quite possible.
Elimelech moved his family to Moab for relief from the famine. However, moves of this nature were often more dangerous than they were helpful. He took his family into a pagan country, and his sons were of marriageable age. There was the danger of their marrying foreign women who could turn their hearts away from Jehovah, the only true and living God (cf. Deut. 7:1-4; I Kings 11:1-13). After the father died, the sons did in fact marry Moabite women. They lived in the land of Moab for about ten years. Then, both sons passed away also.
"Then she [i.e., Naomi] arose with her daughters-in-law that she might return from the country of Moab, for she had heard in the country of Moab that the LORD had visited His people by giving them bread. Therefore she went out from the place where she was, and her two daughters-in-law with her; and they went on the way to return to the land of Judah. And Naomi said to her two daughters-in-law, 'Go, return each to her mother's house. The LORD deal kindly with you, as you have dealt with the dead and with me. The LORD grant that you may find rest, each in the house of her husband.' So she kissed them, and they lifted up their voices and wept. And they said to her, 'Surely we will return with you to your people.' But Naomi said, 'Turn back, my daughters; why will you go with me? Are there still sons in my womb, that they may be your husbands? Turn back, my daughters, go--for I am too old to have a husband. If I should say I have hope, if I should have a husband tonight and should also bear sons, would you wait for them till they were grown? Would you restrain yourselves from having husbands? No, my daughters, for it grieves me very much for your sakes that the hand of the LORD has gone out against me!' Then they lifted up their voices and wept again; and Orpah kissed her mother-in-law, but Ruth clung to her" (Ruth 1:6-14).
Once the famine was over in Judah, Naomi had no reason to remain in Moab any longer--especially since her husband and sons were all deceased. She wished the two young women well and encouraged them to return to the homes of their mothers. It is obvious that both Orpah and Ruth loved Naomi dearly, for their initial desire was to go with Naomi to Judah, even after she encouraged them to remain in Moab to remarry.
Naomi's words in 1:11-13 seem to imply that she believed that there was only one way that these women would ever get married again if they came back with her to Israel--that is, if she herself had more sons for them. She recognized that this simply was not going to happen. She considered herself too old to marry again. Essentially, Naomi wants Orpah and Ruth to understand that following her back to Judah would most likely mean a lifetime of widowhood for them. She does not expect any Israelite man to marry these foreign women in the land of Judah.
Orpah was persuaded to go back home. She kissed Naomi, left, and there is no further record of her activities. Ruth, on the other hand, was resolute. She chose to remain with Naomi. Here is where the love story begins!