What problems did Odysseus' absence create?

Odysseus' twenty year absence from Ithaca (10 years fighting the Trojan war, 10 years attempting to return home) caused several problems to occur in Ithaca. Most of these problems were related to Penelope's suitors.

First, Odysseus' absence caused a mob of suitors to swarm his house and threaten his family unit. Many people believed Odysseus was dead, so all the eligible bachelors began attempting to court Penelope, Odysseus' wife. Their advances became increasingly aggressive, and had Odysseus' return been delayed any longer, she may have been forced to choose a new husband. Moreover, there is evidence that Telemachus--Odysseus and Penelope's son--was in danger, because he had to secretly leave Ithaca when he wished to inquire about his father's fate.

Odysseus' wealth was also greatly diminished as a result of his absence. The suitors had essentially taken up residence in his house and had wasted so much of his money feasting that Telemachus was at risk of losing his entire inheritance. 

Finally, Odysseus was forced to wage a bloody war against the suitors to reclaim his throne, home, and wife.