Here's is a history, thanks to Gallup going back to 1992 on the country being divided.
As you see during Bill Clinton the percentage of those who think our country is divided rose from 63% to 66%. Only 9-11 brought us together under G.W. Bush, it fell to 24%. It took an external threat to unite us politically. Those who thought we were divided then rose to 65% within 3 years after 9-11. Back to normal politics. Under Obama the percentage of those who thought we were divided rose from 66% to 75% and is now at 77%.
You can see that 88% of Republicans think Trump is doing more to unite the country, 43% of independents go along with that thinking vs. 12% for the Democrats. If you scroll down, you'll find that when we have a Democratic president, Democrats think their president is doing more to united the country, Republicans think the Democratic president is doing more to divide the country and vice versa. Republican president, Democrats state the GOP president is doing more to divide while Republicans say their president is doing more to unite.
This leads me to believe whether a president is trying to unite or divide is purely a partisan thing. I'll add one more thing which I think is adding to the percentage of division. That is our biased media which has taken sides in our political battles. They no longer report on them, they've taken sides and give the news according to their slants or even political agenda. This is especially true with the three cable news networks. Nationally 64% state the media is the reason for the divisions or causing the division, 56% say Trump. There is a huge difference by party. 80% of republicans say the media is the cause for the division vs. 25% saying Trump. Democrats, 46% say the media, 88% Trump. Independents 67% say the media, 54% Trump. Again, purely partisan on this subject.