Interstellar Empires And Cosmic Events

Interstellar sf need not be about clashes between interstellar empires! See Poul Anderson's:

Rustum History

Kith History

Tau Zero

Starfarers

Geneisis

Harvest of Stars Tetralogy

All of these works involve slower than light interstellar travel which tends to rule out imperialism. Future histories involving faster than light travel are more likely to feature interstellar empires. Despite his much smaller output, James Blish has more such empires than Anderson. Blish argued that interstellar distances meant that such conflicts could remain inconclusive.

Blish's "This Earth of Hours" ends as conflict is about to begin between the telepathic Central Empire and the Terrestrial Matriarchy.

Blish's second Jack Loftus novel ends as conflict is about to begin between the Heart Stars and a new alliance led by Earthmen, dolphins and energy beings called Angels.

In Blish's "A Style in Treason," there is a long term stand-off between the Green Exarchy and High Earth.

In Blish's Cities in Flight, Arm II of the galaxy is successively ruled by an unnamed civilization, by the Vegan Tyranny, by the Earthman culture and by the Web of Hercules. While Earth is ascendant, it favours interstellar trade by flying cities as against several interstellar empires proclaimed by rebel Admirals etc.

In Anderson's Technic History, the Terran Empire and the Merseian Roidhunate wear each other out so that neither of them is still around in a story set several centuries later.

Anderson also focuses on cosmic events:

Beta Centauri captures rogue planets;

a rogue planet orbits close to Beta Crucis;

a supernova covers a planetary core with supermetals;

a rogue planet impacts the star Saxo;

another star passes through the system of Siekh, disrupting planetary orbits;

a supernova blasts the hydrogen and helium away from a super-Jovian planet;

a globular cluster on an eccentric orbit between the galactic centre and the rim periodically gathers interstellar matter which condenses into new stars whose close proximity causes intense radiation and frequent novae. 

The Beta Crucis rogue, the supermetals planet and the globular cluster are sources of immense wealth.

Anderson excels with these events.