I do not care who started it decades ago. I care about who is engaged in it now. They are both clearly engaged in it. The right and it's tea party and religious pandering...the left and it's identity politics dividing by race, orientation... both actively attack those on the other side. I remember the "Obama is a Muslim" and "Republicans want you to die quickly" attacks for example.
Well many things have changed since then that would affect the historical records and how that compares to modern climate. Social media, TV and internet access, firearm tech, different social groups with different aims as opposed to the "good ol' days of yore", improvements in personal transportation...
So there are always variable and things in play as far as that goes.
Yeah cause its the way business is done these days if you catch my drift. Always looking to wedge your opponent on a hot button issue that feeds the media and the news cycle.
If you look at the way parties used to campaign, with a manifesto, broad community support and involvement, speeches at factories and so on, it was a more organic process. These days most political parties are more like media organisations, substance and consultation with the community and their constituency is not as important as dominating the media cycle, spinning the days events and finding media friendly sound bites. It cheapens the whole process and these parties only really exists to further their own interests.
That said politics by nature should be an adversarial process but the language and nature of todays politics is really appalling, it also stops people innovating and taking risks and suggesting difficult solutions to complex problems because their opponent will workshop a cheap line and attack them with it. This culture is a big part of what is wrong with politics, especially in the English speaking world.