Damn, I was just about to go to bed, oh well...

Imagine an alternate Earth in a parallel Universe. Imagine being transported to this other Earth and then reading some of the recent history. There you learn some surprising things have happened lately. The chairman of the Walmart corporation was assassinated. A bomb killed dozens in a theater in Barcelona, followed by additional bomb attacks over the next several years (more than 80 bombs over a period of only 7 years, including six in one week). During the Prime Minister of Spain's wedding a bomb nearly killed the PM while 2 dozen spectators lost their lives, and over a hundred were injured. There was a brazen attack against the parliament of France with a shrapnel bomb exploding in the parliamentary chamber, but fortunately no one was killed, though many were injured. A cafe in Paris was bombed, killing one and injured 20. A coordinated set of bombings in New York, Boston, Philadelphia, Pittsburgh, Cleveland, New Jersey, and Washington DC struck on the same day, within a timespan of 90 minutes of one another, striking at prominent government officials including the Attorney General, fortunately the bombs did not achieve their aim, but only just. A car bomb on Wall Street killed 30 and injured hundreds. The offices of the Los Angeles times were bombed, killing 21 employees and injuring about 100 more. The French President himself was assassinated. The American President was assassinated!

This is not, however, a record of the events of some parallel Earth, these things actually happened (or very close to what I described), on our Earth, during a tumultuous period around the turn of the 20th century. During that time there was a great deal of unrest in the western world with many people attempting to overturn the conventional status quo in favor of something purportedly less exploitative of workers. Conflicts between unions, union organizers and union-busting corporations or government frequently became violent. In 1892 a strike of 3,000 steel workers at a plant owned by Andrew Carnegie devolved into a bloody battle between Pinkertons (private security) and the workers with three Pinkertons and nine workers killed. It took the intervention of state militia to quell the violence. The manager responsible for dealing with the unions so harshly, Henry C. Frick, was targeted by an anarchist who later entered Frick's office and shot him dead. At the time Carnegie's US Steel was the most highly valued corporation, a near-total monopoly of steel production in America.

The story of the bomb in a theater in Barcelona, that actually happened at the opera. 72 of the upper crust of Western Europe were killed or injured in the attack in 1893. Many of the attacks were carried out by anarchists (such as the assassination of president McKinley) and communists. In general, a loose ideological grab bag of folks who were vehemently opposed to the status quo of classism, extreme wealth inequality, and brutal exploitation of the working class by the establishment and corporate interests had decided to take matters into their own hands and attempt to overthrow the established order, by any means necessary. Those forces would later bubble up into outright civil war in many countries throughout Europe (Spain, Russia, etc.), in many other countries they were brutally suppressed down to the ideological level with ruthless violence (even in the US, despite its alleged high value for the rule of law and individual freedoms).

This doesn't touch on a lot of other terroristic acts of other kinds as well. Such as the many acts of terror that kept freed slaves in their place within the racially divided caste system that existed in the US from the end of the civil war through the mid 20th century, most, but not all, such acts concentrated in the South. Or, the many acts of political violence by fascists or partisans during seizures of power in Italy, Germany, and elsewhere during the 1920s and 1930s. Or the many individual acts of terror committed for personal rather than ideological reasons, such as the "mad bomber" in New York, or the Bath School Massacre, and so forth.

The reason why these things seem like a newer phenomenon is due to the relative stability that existed in Western cities during the Cold War.

Can you define what you mean by terrorist attacks? Do you mean attacks targeting civilians or indiscriminate violence in general? Or targeting government/state actors with/without regard for civilian life?