Learn Portuguese (Portugal): Havia muita tensão, e depois houve um protesto exaltado. - There was a lot of tension, and then there was an agitated protest.

They both come from the verb haver, but they use different past tenses to show how the events happened. Havia is the Imperfect tense, which sets the scene: the tension was an ongoing background state. Houve is the Preterite tense, describing a specific, completed event that happened at a distinct point in time: the protest.

If the protest lasted a long time, could I use havia instead of houve for the second part?

Yes, but it changes the story. Using havia um protesto would describe the protest as an ongoing background setting. Because the sentence uses houve, the speaker is telling us that the protest was a distinct, completed event that broke out after the tension.

Why is it muita tensão instead of muito tensão?

The word muito must agree in gender with the noun it modifies. Nouns ending in -são or -ção, like tensão, are almost always feminine in Portuguese. Therefore, we use the feminine form muita.

I recognize exaltado from the English word "exalted". Are they the same?

Not quite! They are often false friends. While exaltado can mean "exalted" in very formal contexts, in everyday Portuguese it means heated, hot-headed, or agitated. An agitated or heated protest makes much more sense here than a praised one.