Rashi (from Megilah 11a): This hints to Malchus Paras, which ruled after Bavel. They eat and drink like a bear, and are fat like bears.

Malbim: This is Malchus Madai u'Faras, which conquered Bavel and ruled after them. A bear is weaker than a lion ? they did not rule over the entire world like Nebuchadnetzar, who ruled over Ashur, Paras and Madai and the 27 nations that Yirmeyah mentioned (Perek 25). In Nebuchadnetzar's dream, he saw Madai u'Faras in the form of silver, which is less [important] than gold and weaker ¹ than it.

Rashi: This enables us to read it like Diva, the Targum of Ze'ev. Malchus Paras is compared also to a wolf ? "Hikam Arye mi'Ya'ar Ze'ev Aravos Yeshadedem."

Rashi: It stood on one side. This hints that after Bavel ceases, Paras will delay one year while Madai rules.

Ibn Ezra (14, citing Yefes): Koresh and Daryavesh killed three big cities on one side of Malchus Kasdim. It is written in the annals of Malchus Paras and Madai.

Malbim: First the bear went on two sides ? sometimes on one side, and sometimes on the other side. Afterwards, it remained standing on one side. After Daryavesh [ha'Midi] died, his son-in-law Koresh inherited the kingship, and then it remained with Paras until the last Daryavesh [ha"Parsi].

Rashi citing Kidushin 72a: Three ribs are in its mouth. They hint to three Medinos that constantly rebelled against it, and made Shalom with it. Sometimes it swallows them, and sometimes it spits them out. "Bein Shinah" ? sometimes they are outside of its teeth, and sometimes inside its teeth.

Rashi: This refers to three kings that will come from Paras ? Koresh, Achashverosh and Daryavesh, who built Bayis Sheni.

Malbim: It seized three kingdoms ? Bavel, Ashur and Madai u'Faras. These are three pillars of the world. This is why Daryavesh appointed three Sarchim on the entire kingdom ? one on each of these three Tzela'os. It held them between its teeth, for a bear eats also other things, not only meat. Initially, Paras did not destroy those whom it conquered, like Nebuchadnetzar did.

Ibn Ezra (14, citing Yefes): This refers to three big cities on one side of Malchus Kasdim that Koresh and Daryavesh killed.

Ibn Ezra (14, citing Rav Sadya Gaon): This refers to Achashverosh ¹ , who wrote letters to eradicate Am Yisrael, who are called "Am Rav v'Atzum."

Malbim: Nevi'im commanded it to eat much meat ? those of Bavel who were killed. They prophesized that they will kill all residents of Bavel. This was not the nature of this bear; it was Hashem's decree. So prophesized Yeshayah and other Nevi'im.