Learn Hardcore Spanish (Latin America): La frontera estaba tranquila porque la policía había organizado un nuevo cruce para peatones. - The border was calm because the police had organized a new pedestrian crossing.

Estar describes temporary states, feelings or conditions.
Ser describes inherent qualities or permanent characteristics.
Here, the border’s calmness is a temporary situation (“the border was calm [at that moment]”), so we use estaba tranquila (estar) rather than era tranquila (ser).

Why do we say había organizado instead of simply organizó?

Había organizado is the pluperfect (pluscuamperfecto) and signals an action that happened before another past action or state.

In the sentence, organizing the crossing happened before noticing that the border was calm.
If you used organizó (simple past/pretérito), it would just narrate a completed action in sequence, without emphasizing “already done” when the border was calm.

Why is la policía singular here? Could we say las policías?

La policía is a collective noun referring to the police force or institution as a whole and takes singular verbs/adjectives.
Los policías refers to the individual officers (plural).
Saying las policías is uncommon—use la policía for the department or force in general.

Why is the adjective tranquila feminine? Do adjectives always match the noun?

Yes, Spanish adjectives agree in gender (masculine/feminine) and number (singular/plural) with the noun they describe.

Frontera is a feminine singular noun, so the adjective must be tranquila (not tranquilo).

What exactly does cruce mean in this context?

Cruce literally means “crossing” or “intersection.” Here it refers to a designated spot where people walk from one side of the border to the other. In English, you could say “pedestrian crossing” or “crossing point.”

Why do we use para peatones instead of por peatones or de peatones?

Para expresses purpose or destination: cruce para peatones = “crossing for pedestrians.”
Por peatones would imply “because of pedestrians” or “by means of pedestrians,” which doesn’t fit.
De peatones could mean “of pedestrians,” as in cruce de peatones, but that construction is less common than cruce peatonal or paso peatonal in many regions.

Could we say paso peatonal or cruce peatonal instead of cruce para peatones?

Yes. Both are idiomatic and often seen on signs:

Paso peatonal = “pedestrian crossing”
Cruce peatonal = “pedestrian crossing”
They’re virtually interchangeable with cruce para peatones, though paso peatonal might sound a bit more formal or technical.

Why is porque one word here? What’s the difference with por qué, por que, and porqué?

porque (one word) = “because” (conjunction).
por qué (two words, with accent) = “why?” (question).
porqué (one word, with accent) = “the reason” (noun).
por que (two words, no accent) rarely appears and usually is part of a longer structure (e.g., “luchar por que…”).
In our sentence we need “because,” so it’s porque.

Why is nuevo placed before cruce? Could we say cruce nuevo?

Adjective placement in Spanish can alter nuance:

Un nuevo cruce often suggests “an additional or different crossing” in the context of an existing network.
Un cruce nuevo simply emphasizes that the crossing is brand-new.
Both are grammatically correct; choosing one over the other depends on subtle emphasis.